U.N. Secretary General Javier Perez de Cuellar announced last night that he will depart for Baghdad tonight on what is likely to be the most important in a flurry of last-chance efforts to avert war in the Persian Gulf before Tuesday's Security Council deadline for Iraq to withdraw from Kuwait.

"I am hopeful this mission of mine will be of some help," Perez de Cuellar said, adding that he expects to meet with Iraqi President Saddam Hussein. "Now I feel it is my moral duty as secretary general of the United Nations, an organization devoted to peace, to do everything to avoid the worst."

The mission was endorsed yesterday by several governments and got a special blessing from President Bush and Secretary of State James A. Baker III after Baker said he had failed to make any progress in his Geneva meeting with Iraqi Foreign Minister Tariq Aziz.

However, diplomatic sources here and in New York said Perez de Cuellar is pessimistic about his chances of persuading Saddam that refusal to get out of Kuwait is moving Iraq inexorably toward a bloody confrontation with the U.S.-led military coalition arrayed against it in the gulf.

Some U.N. sources said they believe the United States wants Perez de Cuellar to undertake the mission primarily in hopes of sidetracking new diplomatic initiatives being fashioned by France and the 12-nation European Community. These plans involve the possibility of promising Iraq an international conference on Middle East problems, including the Israeli-Palestinian conflict, and that idea is opposed strongly by the Bush administration as unacceptable linkage.

Perez de Cuellar, the sources noted, has no mandate from the Security Council to negotiate with Iraq over an international conference or other Iraqi demands and can only remind Saddam of the council's resolutions demanding an immediate, unconditional end to Iraq's Aug. 2 occupation of its smaller neighbor.

"His mandate is clearly restricted: he can clarify, but he cannot negotiate," a senior U.S. official said. Nevertheless, the official denied that the United States is interested in a Perez de Cuellar mission only as a means of blocking the European initiatives. He and other administration officials said Bush, who met with the secretary general last Saturday and spoke with him by phone yesterday, had told him the administration hopes Perez de Cuellar might have more success than Baker in getting hard truths across to Saddam in a face-to-face meeting.

"We know the secretary general is very reluctant to go, particularly if he is going to be part of a crowd of diplomats pouring into Baghdad, and we are not pushing him," one U.S. official said. "But he is clearly our preference to make the try because he is identified with Third World aspirations, he has worked closely with the Iraqis before in mediating a cease-fire in the Iran-Iraq war, and, even though he got stiff-armed when he made an earlier mission there at the end of August, he is more trusted there than any American can hope to be."

Foreign Minister Jacques Poos of Luxembourg, which currently holds the rotating presidency of the EC, said the community had invited Aziz to meet with him and other EC representatives in Algiers "in the next few days." But at a Geneva news conference following his meeting with Baker, Aziz rejected the proposal, citing past slights by the EC. However, he held out the possibility of EC representatives going to Baghdad.

In Paris, French President Francois Mitterrand told a news conference that war could be averted if Iraq announced before Tuesday's U.N. deadline that it had started a withdrawal from Kuwait. Then, he added, Perez de Cuellar and a special force from other Arab countries could oversee completion of the withdrawal.

Mitterrand's government has been working closely with Algerian President Chadli Bendjedid on a Franco-Arab plan aimed at finding a diplomatic alternative to war. However, the principal U.S. allies in the anti-Iraq coalition, Saudi Arabia and Egypt, have been reluctant to cooperate with the plan because they say it would allow Iraq to retain some of the fruits of its aggression.

There has been speculation in the French press that Mitterrand would send his foreign minister, Roland Dumas, to Baghdad if the Baker-Aziz talks failed. But at his news conference, Mitterrand dodged questions about whether a Dumas mission was in the works.

A key point of the French initiative -- and one that has strong support within the EC -- calls for agreeing to Iraq's insistence on an international conference that would try to resolve the Palestinian question. However, the United States has objected, arguing that such linkage would reward Iraq's aggression. Israel opposes the idea of a conference.

Special correspondents Trevor Rowe at the United Nations and Sharon Waxman in Paris contributed to this report.