WASHINGTON (AP) _ In a last-minute overture to avert an invasion, President Clinton authorized former President Carter on Friday to lead a delegation to Haiti to persuade its defiant military leaders to surrender power and leave.

Army Chief Raoul Cedras and his cohorts agreed to receive the delegation, which also will include retired Gen. Colin Powell, former chairman of the Joint Chiefs of Staff, and Sen. Sam Nunn, D-Ga., chairman of the Senate Armed Services Committee. They are expected to go to Haiti on Saturday.

''President Clinton wished to pursue every possible alternative that would allow (the Haitian leaders) to leave without bloodshed,'' a senior administration official said at a White House podium moments after National Security Adviser Anthony Lake publicly announced the mission.

The only purpose of the discussion with the Haitians is ''the means of their departure,'' the official said. The discussions would involve guarantees about the military leaders' assets, travel arrangements and destination.

''This does not alter by one minute or one second the timetable of our military preparations, our preparedness to act or the urgency of the situation in general,'' the official said.

Administration officials said an invasion force was ready to strike. Yet, it was certain that troops would not go in at least until the delegation has completed its business.

Independent of the White House, Carter has been in touch for some time with Cedras, the junta's leader, the official said. Carter contacted Clinton and said he thought direct talks would be worthwhile.

The official said ''it would be wrong to assume'' that Cedras had signaled a willingness to surrender power, but added that the junta leaders understand that their departure is the only thing the delegation is authorized to discuss.

Carter has carried out frequent quasi-diplomatic missions to Africa, Latin America and elsewhere. Most recently, he went to North Korea as Clinton's envoy to ease tensions about that country's suspected nuclear program. At the time, there was some criticism that Carter had given too rosy an assessment of North Korea's position.

Nunn has questioned the goal of ''restoring'' democracy in a nation where democracy never took hold. Appearing Friday at a charity fund-raising dinner in Macon, Ga., he didn't seem optimistic about a diplomatic solution. ''I hope we can bring about some resolution,'' he said. ''I think the odds are against it, but I hope so in spite of it all.''

Powell, too, has told associates he opposes an invasion. ''We are making the trip to solve the crisis without the loss of a single Haitian or American life,'' he said Friday night in Ashland, Ohio, where he spoke at a fund-raiser at Ashland University.

Regardless of their personal beliefs, the senior official said, ''They are all very clearly prepared to conduct these discussions within the context of the administration's policy.''

Accompanying Carter, Nunn and Powell will be Lawrence Rossin, the National Security Council's point man on Haiti, and Maj. Gen. Jared Bates, the chief assistant to Lt. Gen. John Sheehan, director of operations for the Pentagon's joint staff.

William Swing, U.S. ambassador to Haiti, said on CNN Friday night the discussions would be only on the ''modalities of the departure'' of Haiti's military leaders.

Madeleine Albright, U.S. ambassador to the United Nations, said Clinton ''wants to leave no stone unturned.'' The questions for Haiti's leaders, she said on CNN, are ''How do you want to get out, where do you want to go, and how can we help you get out?''

Planning for the mission was under way even as exiled President Jean- Bertrand Aristide joined Clinton at the White House with representatives of two dozen nations that have pledged to help end three years of brutal military rule in Haiti.

Reaching beyond the Haitian military chiefs to their followers, Aristide said: ''Stop the violence. Do not be afraid. We say, and we will be saying again and again, no to vengeance, no to retaliation. Let us embrace peace. When? Now. Is it too late? No. The time is now.''

There has been concern about the likelihood of revenge-motivated violence by Aristide's supporters. Clinton applauded Aristide's pledge of reconciliation.

''The hand which you have reached out even in this hour to those who have taken democracy away is critical to your success,'' Clinton told the priest- turned-politician.

Around a U-shaped table in the East Room, flanked by the flags of 24 nations, Gen. John Shalikashvili, chairman of the Joint Chiefs of Staff, briefed coalition members on invasion plans.

Administration leaders made the rounds of television news shows and held briefings at the White House to increase pressure on Cedras and his colleagues. Clinton cancelled a planned Sunday trip to California, increasing speculation about the timing of an invasion.

Behind the scenes, the administration searched for any sign the coup leaders were willing to leave.

However, William Gray, the president's special adviser on Haiti, stressed, ''We will negotiate one thing: their departure.''

Secretary of State Warren Christopher said there was no sign Cedras was willing to go.

''Rumors always swirl in this situation but we don't have any reliable signs yet,'' Christopher said. He said there was still an opportunity for the military leaders to leave.

Defense Secretary William Perry said the administration had picked up signals that ''there are some cracks'' in the Haitian junta. ''Whether these cracks will lead to positive useful actions, it's too early to speculate,'' he said.

U.S. officials had heard reports that police chief Michel Francois had sent his family out of Haiti, Perry said, adding that he knew, but would not disclose, the whereabouts of Cedras' wife.

Jean-Claude Duvalier, Haiti's former ''president for life,'' has been enlisted as an intermediary by the military junta, according to sources, but any role he might have was eclipsed by the Carter mission.

Also Friday, Panama said it would grant political asylum to Cedras if that would prevent a U.S. invasion. ''We would give him asylum with pleasure, but not after an invasion,'' said President Ernesto Perez Balladares.

Aristide tried to undercut the junta's authority by appealing to its followers. ''Members of the military, we will create jobs for you. You will not be isolated. You are the sons of the lands, the nation's citizens. Stop the violence.''

He sought to allay concerns he would cling to power. ''I will not be and cannot be a candidate,'' for re-election once his term ends in February 1996, he said.

Informal planning documents drafted by the Pentagon show the United States intends to spend some $100 million over the next six months to pay the costs of the foreign troops and other personnel enlisted to help in Haiti, according to congressional sources.

While the White House has made no formal request to Congress for the additional money, the planning papers assume U.S. support for the more than 2,000 troops from two dozen countries.

Clinton's plans met criticism from former Vice President Dan Quayle, who said during a speech to the Christian Coalition's conference in Washington that he was ''sending our servicemen in harm's way for no good reason.''

Former President Bush, in Florida campaigning for his son Jeb, the Republican candidate for governor, told reporters, ''I don't know what the vital U.S. interest is in Haiti. Therefore, I hate to see the lives of Americans put at risk. But if we go there, I'll support it 100 percent.''