POINT SALINES, Grenada

In the most dramatic move of his Presidency, Ronald Reagan sent in the Marines and Army to pluck to safety hundreds of Americans from this troubled island and to halt Cuban-Soviet advances in the hemisphere.

The invasion ends the Cuban presence on Grenada and takes out of commission a controversial airfield that the U.S. believed would have allowed Havana and Moscow to extend their power in the Caribbean and Central America.

After evacuating nearly 500 Americans from what he called great peril on the island, Reagan told a nationwide television audience on October 27 that the invasion nipped in the bud a Cuban plot to occupy Grenada.

"We have discovered a complete base with weapons and communications equipment which makes it clear a Cuban occupation of the island had been planned," Reagan said, adding that 600 Cubans had been taken prisoner.

Clandestine caches. The President asserted that American troops had located several arms warehouses, one of which held "weapons and ammunition stacked almost to the ceiling-enough to supply thousands of terrorists."

The speech came as the invaders began mopping-up operations after two days of heavier-than-expected fighting. Ahead now: A period of occupation by American troops, during which Grenada will hold elections for a new government to replace the Marxist regime that the invasion had tossed out of power.

Reagan's goal is to restore democracy quickly to the former British colony, still a Commonwealth member. Pending elections, an interim government will be set up, probably led by Grenada's Governor-General Sir-Paul Scoon.

No deadline has been set for a U.S. pullout, although officials say it could come within weeks-if the British agree to take over a peacekeeping role.

Prisoner policy. An immediate concern is how to return the Cuban prisoners to Havana and what to do with 49 Russian diplomats and Soviet citizensplus a lesser number of North Koreans, Bulgarians and East Germans-who took refuge in the Soviet Embassy.

While the island has been a sore spot for the U.S. for years, the decision to invade apparently came only after six small Caribbean democracies appealed for help in restoring order to Grenada following a bloody mid-October coup pitting Marxist against Marxist.

Nearby states, increasingly alarmed by Grenada's military buildup, expressed the fear that without U.S. help the upheaval and leftist sentiment would engulf the rest of the region.

Despite the request for help by the Organization of Eastern Caribbean States (OECS), the legality of the operation is being questioned seriously in the U.S. and abroad. Washington takes as its authority a 1981 mutual-security treaty among OECS states that permits them to request aid when they are threatened. According to Secretary of State George Shultz, the even more Marxist and hostile government that seized control of Grenada jeopardized the security of neighboring states.
The U.S. rejects charges that the invasion violated the charter of the Organization of American States, a pact that prohibits intervention by members in each other's affairs. Both Grenada and the U.S. belong to the OAS.

What is not in dispute is that Grenada had been in turmoil since Prime Minister Maurice Bishop, a protégé of Cuba's Fidel Castro, was slain along with cabinet members and many civilians on October 19. The killings followed a coup by a radical band of Army officers.

The bloodbath, in  Shultz's words, produced "an atmosphere of violent uncertainty" that posed a serious threat to the safety of the 1,000 Americans living in Grenada. About 800 were students and faculty members at St. George's University School of Medicine. Most of the others were retirees.

A central concern: That 1,000 or more Americans could be seized and held as hostages in the manner of those taken at the U.S. Embassy in Iran. "The nightmare of our hostages in Iran must never be repeated," Reagan declared.

Just one day before the invasion, the junta led by Gen. Hudson Austin cabled assurance that no harm would come to Americans. But in Washington's opinion, the situation was too explosive for the Grenadians to guarantee anyone's safety.

On October 20, Reagan decided to divert to nearby Caribbean waters a 21ship naval force, part of which was carrying Marines to Lebanon. At that time, he said, he was only contemplating evacuating Americans if the situation should worsen suddenly.

Call for aid. The next day, while on a golfing trip to Augusta, Ga., Reagan, Shultz and others continued to discuss the near anarchy in Grenada. About the same time,
ministers from Jamaica, Barbados and five members of the OECS were calling upon Washington for help.

The decision to invade was made October 23, the same day that U.S. diplomats who had visited Grenada returned with disturbing reports of "high anxiety" among American students, an opinion that differed sharply from an earlier reading by university administrators.

Washington's concerns were vindicated by the first of several hundred Americans evacuated from the island to an Air Force base at Charleston, S.C.

Students' views. One medical student, Bill Riffley of Phoenix, Ariz., recounted an ordeal of terror in which Grenadian troops kicked in the door of the house in which he was living with other Americans and held them for 3 hours. "There were about 30 Grenadians with AK-47s," he said. "They said they were there to protect us."

"We thought we could be potential hostages," added student Jeff Geller of Woodbridge, N.Y. "We just wanted to get out, if we could."

The invasion began before dawn on October 25 with 1,200 American Marines, 700 U.S. Army Rangers and 300 more fighters from Barbados, Jamaica, Antigua, St. Vincent, St. Lucia and Dominica.

Secrecy surrounding the operation was almost total. While congressional leaders were informed on the eve of the invasion, they were not told when it would be launched and were not asked to approve the mission. Not even the White House press office was informed.

Reporters were not permitted to accompany U.S. forces to Grenada, and those already there were quickly ordered out. Journalists were allowed on the island only on the third day.

The U.S. forces launched a threepronged assault. Marine units helicoptered to Pearls Airport on the island's eastern shore, seizing the only functioning commercial airstrip. Another Marine force launched an amphibious landing at Grand Mal Bay, north of the capital of St. George's.

Farther to the south, U.S. Army Rangers and units of the 82nd Airborne Division parachuted onto the just completed, Cuban-built airport here at Point Salines. The Rangers immediately came under fire from Cuban positions near the 9,000-foot-long landing strip.

While the Rangers expanded their control with the help of helicopter gunships and jet fighters, Marines moved south from Grand Mal Bay in a pincers movement to seize the capital.

Unexpected reception. After meeting surprisingly heavy resistance, U.S. commanders summoned reinforcements, and troop levels climbed beyond 5,000. Grenada's own small Army did almost no fighting, leaving most combat to the force of Cubans described by Havana as construction workers.

The 500 Cubans the Americans expected to encounter turned out to be upward of 1,100, armed with rifles, Soviet-made antitank weapons, antiaircraft guns and machine guns. "For people who were supposed to be construction workers," said one American official, "they fought very well."

U.S. forces overran a Cuban military facility, capturing a Cuban colonelapparently a recent arrival in Grenada-along with a large amount of arms, communications gear and secret papers.

Enough weapons were found, said one U.S. Army colonel, "to arm a division of troops. This should dispel any idea that it was a simple construction project." The cache included crate upon crate of Soviet AK-47 machine guns, rocket-propelled grenades, ammunition and large antiaircraft guns.

After four days, American troops still were trying to flush out the remaining Cubans. But by the weekend, the main battle for Grenada was over and the island controlled by the invaders.

Left unclear was the fate of General Austin, the Grenadian leader, who was reported to be holed up on the southern end of the island with a number of hostages of unknown nationality. The general, with his supporters, was said to be demanding safe passage to Guyana.

Casualty Count. At least 11 U.S. servicemen were killed in the invasion and 67 wounded. Seven were missing. A dozen Cubans and a number of Grenadian civilians also died. The captured Cubans will be sent back to Havana.

The chance to strike against Cuba through Grenada was a long time in coming. The island came under leftist rule in 1979 in a coup staged by Bishop and has become increasingly tied to Havana and Moscow in the years since.

The Reagan administration has charged that Havana had ambitions to turn Grenada into a puppet state, from which it could export Communist revolutions to other Caribbean islands.

U.S. concern deepened when Cuba began building the runway on the southern tip of the island. While Bishop insisted it was for tourism, U.S. officials feared the airstrip-big enough to land long-range Soviet bombers-would permit Moscow to increase its pressure in the Caribbean and to ship weapons to Marxist insurgents in Central America.

Soviet transports already fly regularly into Cuba with arms for both Havana and Nicaragua. A landing strip on Grenada, officials say, would give them a refueling stop that would allow them to bring in even heavier loads. The runway also would have given the Soviets an airfield for fighter operations that could extend over Central America as well as northern South America.

Castro, who had been at odds with Austin over the killing of Bishop, seems resigned to his losses. Grenada, he said, is "an occupied and invaded country where we have nothing to do."

But the latest chapter in Grenada's history is far from over. With radicals going underground and vowing to fight on with hidden arms caches, the U.S. could find that American troops must remain here for a far longer stay than anyone in Washington suspected when giving the order to invade.