By CHRISTOPHER MARQUIS and LYDIA POLGREEN
 
WASHINGTON, Feb. 19 — As Haiti's rebellion spread, the Bush administration took a more active role Thursday in trying to broker a political settlement, and urged Americans to leave the country.

The administration's shift came just days after officials had called on Haitians to assume responsibility for their crisis and seemed prepared to let regional diplomats take the lead in negotiating a peaceful settlement.

But, under growing pressure from relief agencies and human rights groups, the administration brought together diplomats from the Organization of American States, the Caribbean Community, the United Nations and France to draft a proposal for ending the violence with specific steps that the Haitian government and its opponents could take.

In addition, the Pentagon announced it would send a small military team to Haiti to determine the risk to the United States Embassy there at the request of the American ambassdor, James B. Foley.

The State Department urged Americans, including members of the Peace Corps, to leave Haiti because of "a steady deterioration of the security situation." The department also imposed a nighttime curfew on its employees and restricted them to Port-au-Prince, the capital.

At least 57 Haitians have died since the violence began two weeks ago. International relief officials have expressed concern that demonstrators may touch off a food crisis by interfering with deliveries.

Until now, the Bush administration has discounted the possibility of sending in troops, even as it remains alert to the potential for a refugee exodus bound for Florida.

Secretary of State Colin L. Powell said earlier this week the administration had "no enthusiasm" for sending in American forces. France and Canada have volunteered to send police forces, but only in the context of a political solution to the crisis.

Working by telephone in concert with their regional allies and France, administration officials on Thursday put the final touches on a plan that called on President Jean-Bertrand Aristide to appoint a new government, strengthen the police and release detainees, while requiring that his opponents disarm and enter a political dialogue, officials said.

Mr. Powell said Mr. Aristide's resignation was not part of the plan, though he left open the possibility that the president might step down under a negotiated settlement.

"If an agreement is reached that moves that in another direction, that's fine," Mr. Powell told Sam Donaldson in an interview on ABC Radio. "But right now, he has no intention to step down, and since he is the elected leader of Haiti, we should not be putting forward a plan that would require him to step down."

A defiant Mr. Aristide, speaking at a ceremony at the National Palace in Port-au-Prince in honor of policemen killed since the uprising began, told a somber crowd that he would not cede the presidency.

"I am ready to give my life if that is what it takes to defend my country," he said.

A senior foreign diplomat said Haiti's crisis was complicated by the ambivalence many officials felt toward Mr. Aristide, who refused to hold new parliamentary elections after allegations of fraud in 2000.

"It's very difficult that people put their forces at risk to defend that," the diplomat said. "It's not a full democracy."

Mr. Aristide has repeatedly said he will serve out his term, which ends in 2006. He became Haiti's first elected president in 1990; he was ousted in a coup, then reinstated by American forces in 1994. Since then, his relationship with the United States has been strained, with American officials challenging what they say is his uncompromising style and rule by intimidation.

Bush administration officials say Mr. Aristide has already embraced an accord put forth by the Caribbean Community, or Caricom, though the details of that document have not been made public.

The Caricom accord, which is the basis for the proposal being drafted, calls for the appointment of a new prime minister who would be neutral and independent, a government of national unity and the establishment of a new electoral commission, officials said.

Some political analysts said such changes would be difficult to carry out in a country in turmoil like Haiti, and they noted that many Aristide opponents say they would accept nothing less than his departure.

The Haitian capital has remained largely calm, but panic seeped deeper into other Haitian cities and the countryside as antigovernment militants gathered in the north.

In St.-Marc, a port city north of the capital, where pro-government supporters and anti-Aristide militants have battled for two weeks, police officers have been replaced by men toting machine guns and wearing military fatigues.

"These are not police," said one merchant in the city, using a Creole word that means "monster."

Guy Philippe, a former police chief who has been accused of plotting a coup and who returned from the Dominican Republic to command a rebel force, told reporters in Gonaïves that he and his 300 men were planning an assault on Port-au-Prince.

"If Aristide doesn't leave, we will march on the capital," Mr. Philippe said on Radio Vision 2000.

In Cap Haitien, Haiti's second-largest city, militant supporters of the government erected barricades to keep out armed anti-Aristide militias who have taken control of the surrounding countryside. Some police officers refused to leave their barracks to patrol the streets, but others stepped into their place.

Relief groups sent more experts to provide medical assistance to Cap Haitien and other areas of conflict.

Christopher Marquis reported from Washington for this article and Lydia Polgreen from Port-au-Prince, Haiti.