Mr. Posada, a Cuban exile, has long been a symbol for the armed anti-Castro movement in the United States. He remains a prime suspect in the bombing of a Cuban commercial airliner that killed 73 people in 1976. He has admitted to plotting attacks that damaged tourist spots in Havana and killed an Italian visitor there in 1997. He was convicted in Panama in a 2000 bomb plot against Mr. Castro. He is no longer welcome in his old Latin America haunts.

Mr. Posada, 77, sneaked back into Florida six weeks ago in an effort to seek political asylum for having served as a cold war soldier on the payroll of the Central Intelligence Agency in the 1960's, his lawyer, Eduardo Soto, said at a news conference last month.

But the government of Venezuela wants to extradite and retry him for the Cuban airline bombing. Mr. Posada was involved ''up to his eyeballs'' in planning the attack, said Carter Cornick, a retired counterterrorism specialist for the Federal Bureau of Investigation who investigated Mr. Posada's role in that case. A newly declassified 1976 F.B.I. document places Mr. Posada, who had been a senior Venezuelan intelligence officer, at two meetings where the bombing was planned.

As ''the author or accomplice of homicide,'' Venezuela's Supreme Court said Tuesday, ''he must be extradited and judged.''

The United States government has no plan yet in place for handling the extradition request, according to spokesmen for several agencies. Roger F. Noriega, the top State Department official for Western Hemisphere affairs, said he did not even know whether Mr. Posada was in the country. In fact, Mr. Posada has not been seen in public, and his lawyer did not return repeated telephone calls seeking to confirm his presence.

Mr. Posada's case could create tension between the politics of the global war on terrorism and the ghosts of the cold war on communism. If Mr. Posada has indeed illegally entered the United States, the Bush administration has three choices: granting him asylum; jailing him for illegal entry; or granting Venezuela's request for extradition.

A grant of asylum could invite charges that the Bush administration is compromising its principle that no nation should harbor suspected terrorists. But to turn Mr. Posada away could provoke political wrath in the conservative Cuban-American communities of South Florida, deep sources of support and campaign money for President Bush and his brother Jeb, the state's governor.

To jail Mr. Posada would be a political bonanza for Mr. Castro, who has railed against him in recent speeches, calling him the worst terrorist in the Western Hemisphere.

To allow his extradition would hand a victory to President Hugo Ch‡vez of Venezuela, Mr. Castro's closest ally in Latin America and no friend to President Bush.

''As a Cuban, as a freedom fighter myself, I believe he should be granted asylum,'' said Marcelino Miyares, a veteran of the 1961 Bay of Pigs invasion and president of the Christian Democratic Party of Cuba, which is based in Miami. ''But it's a no-win situation for the United States government.''

Orlando Bosch, the most prominent face of the violent anti-Castro wing in Florida, said in an interview broadcast on Tuesday in Miami that he had spoken by telephone with Mr. Posada, who, ''as everybody knows, is here.''

Mr. Bosch, a longtime ally of Mr. Posada's, presented a similar problem for the United States in 1989, when the Justice Department moved to deport him despite resistance from Miami's Cuban-Americans.

The Justice Department called Mr. Bosch ''a terrorist, unfettered by laws or human decency, threatening and inflicting violence without regard to the identity of his victims,'' in the words of Joe D. Whitley, then an associate United States attorney general. Mr. Whitley added: ''The United States cannot tolerate the inherent inhumanity of terrorism as a way of settling disputes. Appeasement of those who would use force will only breed more terrorists. We must look on terrorism as a universal evil, even if it is directed toward those with whom we have no political sympathy.''

The first Bush administration overruled the deportation in 1990; Mr. Bosch remained in Florida. Mr. Whitley, now general counsel for the Department of Homeland Security, declined to comment on the Posada case.

Mr. Posada is said to be sick with cancer, facing mortality. Some veterans of the Bay of Pigs say the armed struggle he represents is dying, too.

''I believe that movement is already dead,'' Mr. Miyares said.

Alfredo Dur‡n, who was captured at the Bay of Pigs and later led a militant anti-Castro group, said that ''after 9/11, it has become inexcusable to defend attacks that could kill innocent civilians.''

''Everybody's renouncing violence except a small group of ultra-hard-core right-wingers,'' said Mr. Dur‡n, now a lawyer in Miami advocating peaceful change in Cuba.

Mr. Dur‡n said that Mr. Posada had never renounced violence and that the question for the United States was whether to denounce him despite his service during the cold war.

Mr. Posada served with the C.I.A. from 1961 to 1967, according to declassified United States government records. He was scheduled to land at the Bay of Pigs, the attack on Cuba ordered by the Kennedy administration, but his mission was canceled when the invasion collapsed. He kept in close touch with the agency after leaving it and joining Venezuela's intelligence service, known by its initials as Disip, where he served as a senior officer from 1969 to 1974, according to the declassified records and retired American officials who served in Venezuela.

In 1974, after a change in government, Mr. Posada set up a detective agency in the capital, Caracas, an office through which many anti-Castro Cubans passed, according to F.B.I. records. He retained his links to Disip, a militantly anti-Castro agency in those cold war days.

Then, amid an international wave of violence by the anti-Castro movement, including the attempted bombing of a New York City concert hall, two attacks shook the United States and Cuba.

On Sept. 21, 1976, in the heart of Washington, a car bomb killed a former foreign minister of Chile, Orlando Letelier, and an American aide, Ronni Moffitt; at the time, it was one of the worst acts of foreign terrorism on American soil. Fifteen days later, a Cubana Airlines flight with 73 people on board was blown out of the sky off the coast of Barbados in the worst terrorist attack in Cuban history.

Mr. Cornick, the F.B.I. counterterrorism specialist who worked on the Letelier case, said in an interview that both bombings were planned at a June 1976 meeting in Santo Domingo attended by, among others, Mr. Posada.

''The Cubana bomb went off, the people were killed, and there were tracks leading right back to Disip,'' said Mr. Cornick, who is now retired.

''The information was so strong that they locked up Posada as a preventative measure -- to prevent him from talking or being killed. They knew that he had been involved,'' said Mr. Cornick, referring to the Venezuelan authorities. ''There was no doubt in anyone's mind, including mine, that he was up to his eyeballs'' in the Cubana bombing.

A November 1976 F.B.I. report, based on the word of a trusted Cuban-American informer, Ricardo Morales, places Mr. Posada at two meetings where the Cubana bombing was plotted. It quotes the informer directly: ''If Posada Carriles talks,'' it says, ''the Venezuelan government will 'go down the tube.''' The document was obtained from government files by the National Security Archive, a private research group in Washington.

Mr. Posada has always denied that he had a role in the bombing. But he was detained by the Venezuelan government for almost nine years in the case -- never formally convicted, never fully acquitted. Finally, in 1985, he escaped his minimum-security confines.

He found work in El Salvador as a quartermaster for the contras, the rebels fighting the Nicaraguan government, whose mission was financed by the C.I.A. and Lt. Col. Oliver L. North of the National Security Council. After that covert operation was exposed in 1986, Mr. Posada landed in Guatemala, working as a government intelligence officer. In 1990, he was nearly killed in Guatemala by gunmen who he has said he suspected were sent by Mr. Castro.

After a slow recovery, Mr. Posada, by his own admission, ran a string of operatives on a series of missions to blow up Cuban people and places. Mr. Posada spoke to The New York Times seven years ago, boasting of what was then his latest exploit, a string of bombings at Havana's hottest tourist spots that terrorized the city and killed an Italian visitor.

Then in November 2000, he traveled to Panama, accompanied by Guillermo Novo, whose conviction in the Letelier bombing had been overturned on appeal; Gaspar JimŽnez, convicted of trying to kidnap a Cuban diplomat in Mexico in 1977; and Pedro Rem—n, convicted of the attempted murder of Cuba's ambassador to the United Nations in 1980.

The moment Mr. Castro arrived in Panama for an international conference, he accused Mr. Posada of plotting against his life. Mr. Posada was seized, along with his three colleagues and 33 pounds of the plastic explosive C-4. Despite Mr. Posada's protest that the case was a sting set up by the Cuban spy service, he received an eight-year sentence in April 2004 for endangering public safety.

Eight months ago, in her last week in office, President Mireya Moscoso of Panama pardoned the men. She cited humanitarian grounds. Ms. Moscoso, who has long had a home in Key Biscayne, has strong social ties to Cuban conservatives in South Florida, said Mr. Dur‡n, the Bay of Pigs veteran.

Her successor, Mart’n Torrijos, criticized the pardon at his inauguration, saying, ''For me, there are not two classes of terrorism, one that is condemned and another that is pardoned.''

Mr. Posada left Panama City and flew to San Pedro Sula, Honduras, bearing a false American passport, according to President Ricardo Maduro, who publicly denounced him.

Mr. Posada left Honduras in a hurry. Mr. Castro said in a recent speech that Mr. Posada then went to the Mexican resort Isla Mujeres and arrived in Florida on a boat owned by a Cuban-American developer in Miami. The Cuban leader offered no proof.

If Mr. Posada wants asylum, ''there will come a time when he will have to come out of the dark,'' Mr. Dur‡n said. ''At that point, he could be arrested for illegal entry.'' But in the present political climate, ''the only place he's safe is here -- even if he's in jail.''

Photos: In Panama in 2000, Fidel Castro displayed a photograph of Luis Posada Carriles. He calls Mr. Posada the worst terrorist in the hemisphere. (Photo by Jose Goitia/Associated Press); Mr. Posada in 1976, the year the bombing of a Cuban airliner killed 73 people. He is a prime suspect. (Photo by Associated Press)(pg. A15); Luis Posada Carriles in prison in Panama in May 2003. (Photo by Teresita Chavarria/Agence France-Presse)(pg. A1)