U.S. TROOPS MOVE IN PANAMA IN EFFORT TO SEIZE NORIEGA; GUNFIRE IS HEARD IN CAPITAL

                ORDERED BY BUSH

                Alternative Government Sworn -- Recognized by Washington

                MICHAEL R. GORDON
                Special to The New York Times

                WASHINGTON, Wednesday, Dec. 20 -- The United States launched a military
                operation in Panama early this morning designed to topple the Government of Gen.
                Manuel Antonio Noriega.

                Reports from Panama said that American troops and tanks were moving on General
                Noriega's headquarters, with mortar and machine gunfire echoing through the city.
                American citizens were ordered by the American military command in Panama to stay
                off the streets.

                Administration officials said the military action was code-named Operation Echo. The
                United States maintains 12,000 troops, most combat forces, in Panama, and additional
                units were flown into the country on Tuesday to assist in the operation.

                First Strike Since Libya

                The operation was the most dramatic foreign policy move of the Bush
                Administration and the first time that United States military forces have
                been sent into combat since the air strike against the Libyan leader, Col.
                Muammar el-Qaddafi, in April 1986. The last large-scale engagement by
                American ground forces took place during the invasion of Grenada in
                October 1983.

                Since taking office, Mr. Bush has been frustrated by failed efforts to
                encourage the ouster of General Noriega, who is accused by the
                Administration of being a major sponsor of illicit drug trafficking. The White
                House was criticized in October for failing to take steps to support an effort
                by elements of the Panama Defense Forces to remove General Noriega.

                It was not clear whether the White House consulted with Congressional
                leaders about the military action, or notified them in advance. Thomas S.
                Foley, the Speaker of the House, said on Tuesday night that he had not been
                alerted by the Administration.

                Troops Flown In

                The first indications that military action was imminent came during the day
                Tuesday when Washington added to its forces in Panama, flying troops and
                equipment into American military bases.

                American troop transport planes, apparently carrying members of the 82d
                Airborne Division from Fort Bragg, N.C., landed in Panama. The exact
                number of arriving troops was not known.

                Administration officials refused on Tuesday to discuss the deployment of
                troops but hinted to reporters that some kind of military action was imminent
                by suggesting that they be prepared for further developments during the night.
                Officially, the Pentagon confirmed only that the 82d Airborne was conducting
                maneuvers, and officials suggested indirectly that they were related to the
                situation in Panama.

                On Tuesday, President Bush presented a business-as-usual image, joining
                singers in Christmas carols at a holiday party at the White House. Brent
                Scowcroft, the President's national security adviser, slipped away from the
                party and joined his deputy, Robert M. Gates, in Mr. Scowcroft's White
                House office late at night. There also were late-night meetings in the Pentagon.
                Earlier in the day, Mr. Bush met in the Oval Office with top advisers, including
                Defense Secretary Dick Cheney; Gen. Colin L. Powell, the Chairman of the
                Joint Chiefs of Staff; Attorney General Dick Thornburgh and Vice President
                Dan Quayle. The White House described the meeting as a discussion of a
                wider role for the military in combating drug trafficking. The meeting lasted
                about half an hour longer than scheduled, an Administration official said.

                Earlier this year, after tensions between the United States and Panama flared,
                President Bush dispatched reinforcements to Panama to augment the 12,000
                American troops stationed there. No military action was taken at the time.

                The latest troop movement came as the Administration described the situation
                in Panama as deteriorating, and members of Congress urged the Government
                to respond with caution to the killing of an American Marine lieutenant.

                The State Department spokeswoman, Margaret D. Tutwiler, said the United
                States was taking General Noriega's declaration of war last week more
                seriously after the killing on Saturday night of the lieutenant and the wounding
                of another officer at a roadblock.

                ''Noriega's irresponsible declaration of a state of war last week, followed only
                hours later by indiscriminate and unprovoked violence against Americans
                clearly increases tension in Panama,'' Miss Tutwiler said. ''We find the
                unwarranted use of violence against Americans by the Noriega regime
                unacceptable.''

                'Very Difficult Atmosphere'

                She added that Panama's declaration of a state of war against the United
                States last Friday has ''a little different meaning right now in light of events that
                are going on down in Panama.''

                The Pentagon spokesman, Pete Williams, described the situation as
                ''deteriorating,'' while the White House spokesman, Marlin Fitzwater, said the
                Bush Administration continued to leave open the possibility of military action.
                ''What you have is a very difficult atmosphere in Panama right now,'' said Mr.
                Williams, adding: ''Things are very tense. People fear for their lives in Panama
                right now.''

                Security in front of the Panamanian military headquarters appeared lighter than
                in recent days. A military vehicle on which a machine gun was mounted was
                pulled back this evening. But nearby streets remained barricaded, and soldiers
                were stationed along key roads behind sandbags and stacks of tires.

                United States security officers briefly detained two reporters and a
                photographer who entered the base to check rumors that United States
                troops were massing in preparation for a strike. The officials seized the
                journalists' notes and film and, ignoring repeated requests, insisted on reading
                the notebooks.

                At several times, the man who appeared to be the commander of the group
                promised to identify himself and his unit after finishing the search of the
                journalists, but he then reneged. ''I guess I lied, didn't I,'' he said. Mr. Williams
                said Tuesday that elements of the Army's 18th Airborne Corps were
                conducting emergency deployment readiness exercises.

                The 18th Airborne is the Army's fast-reaction force and includes paratroopers
                of the 82d Airborne Division.

                ''We are not saying definitively whether the exercises are or are not related,''
                said one Pentagon official. Another official said that while there were enough
                American troops on the ground in Panama to defend American interests, it
                was to the advantage of the United States in such a situation to have such an
                exercise under way.

                'It Is a War of Words'

                ''I certainly can't rule out psychological warfare,'' the official said when asked
                if the exercise was intended as a show of force. ''It is a war of words and a
                war of nerves at this stage and one that is waged diplomatically and
                psychologically and, if need be, militarily.''

                In May, President Bush ordered about 1,800 soldiers and marines sent to
                Panama to reinforce 10,300 American troops already there and to protect
                American lives.

                The United States has also been conducting military exercises in Panama this
                year that American officials say have been held to exercise Washington's
                rights to defend the canal under the 1979 Panama Canal Treaties, but which
                some observers say are also intended to put psychological pressure on
                General Noriega.

                The exercises include motorized patrols across the Bridge of the Americans
                near Panama City, amphibious operations across the canal near the Pacific
                Ocean entrance to the canal and flying troop reinforcements into Howard Air
                Force Base.

                Following the deployment of troops and the exercises, incidents of harassment
                against American servicemen dropped significantly.

                Some Urge Caution

                On Capitol Hill, some lawmakers urged President Bush to use caution in his
                response to the shooting death of the marine officer, while others emphasized
                the need for the President to send an unambiguous message to General
                Noriega that a pattern of aggression against the United States would not be
                tolerated.

                Senator Christopher J. Dodd, a Connecticut Democrat who is the chairman
                of the Western Hemisphere subcommittee of the Senate Folreign Relations
                Committee, said on the NBC News program ''Today'' that he hoped
                President Bush would not act abruptly because of criticism in October for
                failing to intervene during an abortive coup attempt in Panama. ''My concern
                would be that some of the political advisers around him are reminding him of
                those headlines and may cause him to act precipitously here,'' Senator Dodd
                said. Senator Richard G. Lugar of Indiana, a senior Republican member of
                the Foreign Relations Committee, said that caution was important, but added
                in a statement: ''We need to avoid the appearance of acquiescence that might
                embolden Noriega and lead to future American and Panamanian casualties.
                There are measured options, military and otherwise, that would inconvenience
                Noriega and they ought to be considered promptly in the wake of
                unnacceptable activities of the Panamanian Defense Forces.''

                The Pentagon identified the marine who was killed as First Lieut. Robert Paz,
                25 years old, of Dallas.

                The White House said the killing of the American officer, the first by
                Panamanian forces, was part of a coordinated campaign that began when the
                National Assembly of Representatives declared the country at war with the
                United States. His shooting death was one of several incidents of harassment
                of American servicemen last weekend.

                In one incident Saturday night, according to Pentagon officials, an American
                officer and his wife were arrested by Panama's military. The officials said that
                in four hours of interrogation, the naval officer was beaten and repeatedly
                kicked in the head and groin and threatened with death as loaded pistols were
                pointed at his head. His wife, the officials added, was slammed against a wall,
                sexually threatened and required to stand with her arms over her head until
                she collapsed.

                In another incident over the weekend, a Panamanian soldier loaded his assault
                rifle and pointed it at the stomach of an American military policeman who was
                on patrol.

                The Pentagon said that a United States Army lieutenant who wounded a
                Panamanian traffic officer Monday was apparently not authorized to carry a
                sidearm, was in civilian clothes at the time of the shooting, and that the
                incident was under investigation.