U.S. Ambassador Clayton E. McManaway Jr. held a surprise meeting late this afternoon with Haiti's embattled President Jean-Claude Duvalier, adding to speculation sweeping the capital that Duvalier was preparing to flee the country in the face of popular unrest.

The unscheduled meeting, held at Duvalier's request, lasted one hour at the National Palace in the center of town, according to a U.S. Embassy spokesman, who gave no further details.

While there was no official suggestion that the meeting was connected to a possible departure by Duvalier, it was linked in Port-au-Prince's highly charged political atmosphere to the fact that it came one day after the governments of Greece and Spain said Duvalier had requested political asylum in those countries and was turned down.

Haitian government officials today called those reports "ridiculous," but the Europeans stood by their earlier statements. Reports of the asylum requests were broadcast here by the Voice of America, causing a further political stir.

The United States has no official position on whether to grant political asylum to Duvalier, and he has never requested it, according to the U.S. Embassy spokesman, Jeffrey Lite.

[In Washington, State Department officials said Duvalier had not requested asylum or a visa to the United States, nor had he asked whether such requests would be accepted. "He's still in power, and he's still there," one said.]

Despite all the signs, analysts here continued to treat cautiously reports of Duvalier's imminent departure, since there have been false reports in the past that he already had fled the country or had headed to the airport, then turned back.

Some longtime observers here recalled that his father, Francois Duvalier, had falsely leaked news of his own departure as a ploy to test the loyalty of his aides.

When new protests erupted here last week, the U.S. Embassy received reports placing Duvalier in Monaco, Morocco and the U.S. naval base at Guantanamo Bay, in Cuba.

"Separating fact from fiction is a cottage industry in Haiti," said one diplomat.

Despite wanting to avoid yet another false alarm, some analysts here have predicted that Duvalier would leave the country before Sunday, the start of Haiti's annual pre-Lenten carnival.

Each year, hundreds of thousands of Haitians pour into the capital's streets for three days of Mardi Gras festivities, including parades through the streets that pass directly in front of the presidential palace.

Foreign and Haitian observers here speculated that with tensions running high because of the mass protests and the declaration of a state of siege, the parades could turn into massive antigovernment demonstrations that would be too large for even the heavily armed security forces to control.

The Reagan administration has been applying subtle but increasing pressure on Duvalier as his position here appears to have become less tenable.

The heightened U.S. concern over Duvalier's second-generation dictatorship began Thanksgiving Day, when Army troops shot and killed three students in the town of Gonaives.

The students were participating in demonstrations protesting abject poverty, high unemployment and the unequal distribution of wealth.

A fourth youth later died from beatings he received that day from troops, according to diplomatic sources.

The protest against Duvalier erupted again in early January and heightened last week before the state of siege was declared.

Last week, the State Department declined to certify that Haiti was making progress on human rights, a step that means the loss of about $7 million in American aid for this heavily aid-dependent nation.

Since 1982, when Congress first imposed the requirement that Haiti make progress on human rights before receiving aid, the State Department had certified such progress regularly.

The pressure intensified still further with Secretary of State George P. Shultz's recent remarks that Haiti should move toward a democratically elected government.