By TONY SMITH
 
ORT-AU-PRINCE, Haiti, Feb. 24 — President Jean-Bertrand Aristide said today that he would not give in to rebel demands to step down and he appealed to opposition leaders to accept a proposed plan that would stop the rebel advance on the capital and avoid further bloodshed in the Caribbean nation.

American marines manned positions today to secure the United States Embassy, having arrived in Haiti on Monday after rebels consolidated their control of the island's second largest city, Cap Haitien, over the weekend. Government ministers began casting about for secure hiding places and others vowed to repel the insurgent advance.

"If they come to Port-au-Prince, you will have thousands of people killed," Mr. Aristide said, speaking calmly at a news conference in the presidential palace. "I would like to see them neutralized rather than have that bloodshed."

Mr. Aristide called on the international community to accelerate the implementation of a plan to reinforce Haiti's police force, and he called on Haitian citizens to defend the city in case of attack.

Haitian opposition leaders have told Secretary of State Colin L. Powell that they are having a hard time committing to the proposed power-sharing agreement, which has been accepted in principle by Mr. Aristide. The problem, they say, is that they would lose the respect of their supporters by allowing Mr. Aristide to continue in office, even in a titular role.

Political opposition leaders in Port-au-Prince on Monday took 24 hours to examine a peace plan presented by the Bush administration and its allies.

"I expect my brothers from the opposition today to give a positive answer which will create a good bridge between the government and the opposition," Mr. Aristide said.

"It is time for the opposition to stop the violence and share some responsibility," he said.

Men who were dressed in civilian clothes manned makeshift barricades on the streets of the Haitian capital. searching cars but letting them pass through.

Mr. Aristide read a list of towns in the north of the country that had fallen to the rebels, confirming among them the fall of Port-de-Paix.

In Cap Haitien, residents have pillaged and burned any symbol they could find of Mr. Aristide and his party, Lavalas, exacting chaotic revenge on a government they asserted had terrorized them.

Louis-Jodel Chamblain, leader of the rebel troops, said their capture of Cap Haitien, a northern city whose outskirts were the birthplace to the slave uprising that created the world's first black republic 200 years ago, was a symbol of the rebels' intention to wrest control of the entire nation and expel the embattled president. "Cap Haitien is a symbol of Haiti's freedom," Mr. Chamblain said. "This fight is to liberate the Haitian people under the regime of Jean-Bertrand Aristide."

There were indications on Monday that the opposition could accept the peace plan, which was put forth this weekend by Roger F. Noriega, the assistant secretary of state for Western Hemisphere affairs.

Over the weekend, Mr. Powell called a leader of the opposition, André Apaid, to urge him to sign onto the agreement, and American diplomats made similar contacts with rebel leaders, officials said. "We told them if they need more time, to take more time," a senior State Department official said.

Under the proposed peace accord, put together by the United States, France and the Organization of American States, a three-party commission would be set up to appoint a new prime minister and a government of national unity. Mr. Aristide would remain as president.

The international community would take part in the commission and serve as a referee between the president and his enemies, according to officials briefed on the offer, which has not been made public.

The new government would lay the groundwork for parliamentary elections some time later this year and presidential elections toward the end of Mr. Aristide's term in 2006. It would also oversee a changeover in the leadership of the police and set up ground rules for opposition protests and rallies.

Whatever happens in the peace talks, the taking of Cap Haitien has for now put the rebels in control of not only half the country but also Haiti's heartland. The rebels also control Gonaïves, the city where Haiti's freedom from France was proclaimed on Jan. 1, 1804.

Not even two months ago, Mr. Aristide presided over a chaotic bicentennial celebration in Gonaïves, at which he cast himself as the true heir to Haiti's slave soldiers. Those fighters delivered such rattling defeats to Napoleon's imperial army that the French emperor gave up his American colonial ambitions, selling the Louisiana Territory to the United States.

But on Monday, as rebel soldiers patrolled the city and residents sacked the houses of the president's allies, Mr. Chamblain, the rebel military leader, cast Mr. Aristide in the role of the colonial oppressor. "Our objective is to liberate Haiti because we consider Aristide like LeClerc," Mr. Chamblain said, referring to Gen. Charles LeClerc, Napoleon's brother-in-law, whom the emperor sent to quell the slave revolt.

It was a stark reversal of fortune for Mr. Aristide, who had counted Cap Haitien as one of his strongholds.

Lydia Polgreen contributed reporting for this article