Updated

Haitian President Jean-Bertrand Aristide (search) may have miscalculated when he chose not to aggressively pursue a peace deal with his opponents two weeks ago, U.S. officials said Monday as the Haitian leader's position grew increasingly perilous.

In the interim, forces opposed to Aristide have steadily strengthened their position and now have less incentive to negotiate than they did earlier this month, the officials said.

U.S. officials were awaiting word from opposition groups on a peace proposal set forth on Saturday by the United States and European, Latin American and Caribbean countries. Aristide accepted the proposal. But opposition leaders have indicated that no agreement was possible without the president's resignation.

The administration nevertheless remained hopeful.

"We are looking to the opposition to give us a response on their participation in this plan," State Department spokesman Richard Boucher said.

In Port-au-Prince, opposition leaders promised a final answer by Tuesday.

Boucher said the outside mediators are drafting a statement that would commit them to monitoring compliance with an agreement and serving as guarantors. Both sides should understand, Boucher said, that "we will be involved every step of the way."

The proposal presented on Saturday would build on a plan that was drawn up by the 15-nation Caribbean Community at the end of January.

Aristide accepted the plan but the administration says he has done little to carry out its terms. Boucher noted that the plan involves changes in key government personnel, including the appointment of a prime minister.

The administration is showing growing concern over the situation in the troubled country. On Saturday, the State Department ordered the departure of nonessential embassy personnel and of family members.

On Monday, 50 U.S. Marines with anti-terrorism training were dispatched to Port-au-Prince to help protect U.S. facilities. The Homeland Security Department halted on Monday some deportations of undocumented Haitians back to Haiti by commercial airliner because of the unstable situation.

The outlook for Aristide has looked bleaker in recent days, officials said, with the takeover of the country's No. 2 city, Cap-Hatien (search), by rebels on Sunday and reports of frightened cabinet members looking for places to hide.

However, U.S. officials said the armed rebel groups would face far more resistance if they attempt to seize Port-au-Prince. They note that Cap-Hatien was taken virtually without a fight.

Sen. Mike DeWine (search), R-Ohio, who has followed Haiti closely over the years, warned that disaster may lie ahead unless the peace plan is implemented.

"It is certainly not out of the realm of possibility that there will be a bloodbath in Port-au-Prince," DeWine said in a speech on the Senate floor.

Remissainthe Ravix, a leader of one of the armed groups, said in Port-au-Prince that Aristide made a big mistake years ago when he did not disarm the military when he demobilized it.

"There's no such thing as the former Haitian army now," Ravix said in an AP interview, "We have the weapons and the expertise to take the country. Nothing can stop us."