By GINGER THOMPSON
 
MANAGUA, Nicaragua - It has been more than two decades since this tiny nation of five million people and its revolutionary strongman, Daniel Ortega, kept Washington awake at night. In recent months, new fears, but the same old politics, have revived that tossing and turning.

Mr. Ortega, one of United States' fiercest opponents during the cold war and the entrenched leader of the leftist Sandinista National Liberation Front, has opened his fourth campaign for the presidency. Washington is worried once again that its old nemesis might win, this time with consequences for a new global war, on terrorism.

Even though the elections here are more than a year and a half away, and even though Mr. Ortega's chances seem slim, the Bush administration is taking no chances and has begun concerted efforts to stop him.

The clearest shot across the bow came in March when the United States suspended some $2.3 million in military aid to Nicaragua to put pressure on the government, and an army with roots in the Sandinista movement, to destroy its arsenal of Soviet-made SA-7 missiles.

But pressure had been building since January, when a sting operation by the United States and Nicaraguan authorities netted two Nicaraguan men trying to sell an SA-7, a shoulder-fired missile that terrorism experts consider a threat to civilian aircraft.

The sting set off alarms among conservative Republicans, and the State Department sent two high-level delegations here to Managua.

In political magazines and Congressional testimony in Washington, cold war alums - almost as masterly at political resurrection as Mr. Ortega - issued strong, although vaguely substantiated warnings about Al Qaeda recruiting operatives in Latin America; about a new "axis of evil" forming across the Western Hemisphere, from Venezuela through Nicaragua to Cuba; about a "destabilization," or a "backslide away from democratic principles" south of the border; about Daniel Ortega serving as a tool to Fidel Castro of Cuba and Hugo Chávez of Venezuela.

The missile issue consumed public attention during Secretary of Defense Donald H. Rumsfeld's recent tour through the region. Mr. Rumsfeld told reporters that Nicaragua's SA-7's "can be operated by terrorists, by revolutionaries and others," who "are anxious and willing to kill people."

A diplomat traveling with Mr. Rumsfeld, and other diplomats in Washington and Managua, made clear that the United States was specifically concerned about the missiles' coming into the hands of the old Sandinista comandante.

"There's no doubt about it, Daniel Ortega is still the pivotal actor in Nicaraguan politics," a senior State Department official said in an interview. "The Sandinista Party that Daniel Ortega represents is not a democratic party. They may play in democratic processes, but it is not a democratic party.

"So if you are hearing that the United States is worried about missiles, and about who might come to power in 2006, there is basis for that."

Nicaragua was once as much an epicenter of United States foreign policy as Iraq is today. This destitute country was transformed by hundreds of millions of dollars into a front line of the global struggle against Communism. On one side was Mr. Ortega's Sandinistas, who had overthrown a 40-year-old dictatorship and allied themselves with the Soviet Union.

On the other were President Reagan's contras, rebels armed and organized by the United States to overthrow Mr. Ortega's Marxist government.

The armies fought each other to a standstill, until both sides agreed to elections in 1990, which Mr. Ortega lost. The Sandinistas demobilized as an army, and it seemed that Mr. Ortega would fade into the political wilderness.

In fact, though the Sandinista leader has not governed the country since 1990, he has been a force in its politics, surviving shifting ideological tides and public accusations of sexual abuse by his stepdaughter in 1998, charges that Mr. Ortega denied and which were later dropped.

Particularly among Nicaragua's desperately poor masses, Mr. Ortega, now 59, has remained popular, and has been able to call on their support to make this country ungovernable when he pleased.

Every one of the three presidents in power here since 1990, beginning with Violeta Chamorro, has had to share power with Mr. Ortega in one way or another in order to keep protesters off the streets and investors in the country.

After Hurricane Mitch in the mid-1990's, nervous foreign donors pressed the president then, Arnoldo Alemán, to negotiate an agreement with Mr. Ortega to put an end to the Sandinista demonstrations hampering the country's recovery.

Mr. Alemán embraced his archenemy, changed the Constitution to give the Sandinistas an almost equal number of seats on the Supreme Court, the Comptroller's Office and in the Federal Electoral Council.

President Enrique Bolaños forged his own alliance with Mr. Ortega as a way to keep political peace after his government convicted Mr. Alemán on corruption charges.

But the terrorist attacks against the United States hardened the Bush administration's stand against its old opponents in the region. At the end of 2003, then Secretary of State Colin L. Powell traveled here to warn President Bolaños to break with Mr. Ortega.

"Nicaragua must look to the future, not to the past." Mr. Powell said during the visit, recounted a prominent Nicaraguan journalist who covered the meeting, Carlos Fernando Chamorro.

That break not only turned out to be disastrous for Mr. Bolaños, it also energized support for Mr. Ortega, who called on the fractured Sandinista leadership to close ranks against the threat of an "imperialist intervention."

Mr. Ortega used his influence over the country's courts to get the obese and ailing Mr. Alemán released from prison to serve his sentence at home. The men then used their control over the Congress - Mr. Ortega's Sandinistas and Mr. Alemán's Liberal Constitutionalist Party controlled 81 of the 92 seats - to go after Mr. Bolaños.

In December, legislators passed a series of measures aimed at reducing Mr. Bolaños's control over the government, including one that prohibits the president from destroying military weapons without congressional approval. That would include the SA-7's.

And as if to leave no doubts that Mr. Bolaños was holding onto the government by only a thread - he has eight sure allies in Congress - legislators called a vote to impeach him, but then withdrew the motion.

"The reason the Sandinistas still have so much power," the senior State Department official said, "is because they got to keep what they stole, they got to keep their guns, and they use democratic processes and their corruption of Nicaragua's judiciary, in cahoots with Arnoldo Alemán, to extort the country."

Mr. Ortega did not accept several requests for an interview. His wife and spokeswoman, Rosario Murillo, suggested that he would agree to the interview if no other people were quoted in the same article.

Still, in extensive talks with Mr. Ortega's supporters and detractors, and in visits to neighborhoods considered Sandinista strongholds, it was hard to tell whether the man who weighs so much on this country's politics and national identity was on his way to recovery, or on his way out for good.

After a brief opening in the mid-1990's, Mr. Ortega shut the Sandinista Party to democratic reforms. Primaries to select candidates since then had been widely judged as little more than charades. And that stranglehold forced most of his old war buddies to abandon him.

Then last month, newspaper polls showed an even more stunning crumbling in Mr. Ortega's base of support. A CID-Gallup poll showed that the Sandinista front was more popular than any other political party. But it also showed that the former mayor of Managua, Herty Lewites, was more popular among Sandinista sympathizers than Mr. Ortega, by more than 20 points.

The poll hit the country hard. Political experts said that Mr. Ortega's alliance with the convicted Mr. Alemán had disappointed his most devout followers, and that his anti-American polemics did not go over well with a population dependent on the United States for investment and remittances from relatives.

"History marks men," said Víctor Hugo Tinoco, a Sandinista leader and supporter of Mr. Lewites. "Daniel Ortega is a man marked by war. And it is practically impossible that anyone who led a country through 12 years of war can win a democratic election.

"People reject symbols of war," Mr. Tinoco added, "And Daniel Ortega is a living symbol."