A "rather optimistic" U.N. chief Kofi Annan engaged in last-chance talks with the Iraqis on Sunday and said he expected a pact in writing that would open suspected weapons sites and prevent a U.S. military strike.

Officials from both sides expressed hope that a formula could be found that would satisfy U.N. Security Council demands for full access to all suspected weapons sites while satisfying Iraqi claims for national rights.As the talks adjourned after 2 a.m. Sunday, Iraqi Foreign Minister Mohammed Saeed al-Sahhaf said they were "going well" and would resume in several hours. But it was clear that obstacles remained. "I think the secretary-general feels some progress has been made," U.N. spokesman Fred Eckhard said. "It's not done yet. We'll try again."

In Washingtion, national security adviser Sandy Berger said Saturday that, while the United States hopes Annan's diplomatic mission succeeds, "U.S. military preparations are proceeding without regard to these talks."

He spoke after a 90-minute meeting with President Clinton and his top foreign policy advisers.

Annan, who arrived in the Iraqi capital Friday, said he was hopeful he would meet with President Saddam Hussein later Sunday. The Iraqi agency said Saddam was briefed on the talks but gave no details.

A meeting by Annan with the Iraqi leader would be a sign that Iraq was prepared to open eight presidential sites to U.N. weapons inspectors.

The U.N. chief began his official meetings at the Iraqi Foreign Ministry. Half of the three-hour Saturday morning session was devoted to a private meeting between Annan and Deputy Prime Minister Tariq Aziz.

Afterward, the full delegations - nine Iraqis and eight U.N. officials - met for another 90 minutes at the Foreign Ministry and then met again for more than three hours late into the evening. Much of the time, though, Annan and Aziz were alone. Early Sunday the two sides held two more hours of discussions before adjourning.

The inspectors are seeking to determine if Iraq has complied with U.N. orders, issued at the end of the 1991 Persian Gulf War, to destroy all long-range missiles and weapons of mass destruction.

That is the main condition for lifting crippling economic sanctions that the council imposed in 1990 after Iraq invaded neighboring Kuwait, touching off the war.

Iraq says it has complied with the orders but that the United States and Britain manipulated the inspections to maintain the sanctions.

The United States, which has deployed 25,000 troops to the gulf region, has said it will refuse any deal that it believes undermines the authority of the U.N. inspection program.

The State Department, meanwhile, issued a warning to Americans in Iraq to "depart as soon as possible." The White House said the warning was routine and should not be taken as a sign that military action was imminent.

On Saturday, Denis Halliday, the U.N. relief coordinator for Iraq, said if a military strike occurred, food shortages would develop quickly because the United Nations did not have enough in stock to feed Iraq's 22 million people.

In a government-organized demonstration, 62 coffins were paraded through Baghdad in a sym-bol-ic funeral for children Iraq says have died recently due to shortages of medicine.

Iran warned Saturday that a military strike will send a flood of Iraqi refugees into Iran, and Turkey rejected a U.N. appeal to leave open its borders for refugees fleeing possible military strikes against Iraq.

Elsewhere in the Arab world, pro-Iraq rallies continued in several West Bank towns and Jordan, where stone-throwing demonstrators injured two policemen and set fire to a state-owned bank. At least 20 people were injured in Maan, Jordan.

An administration official in Washington said that Clinton, during a meeting held at the White House Jan. 24, approved a plan for massive air strikes aimed at Baghdad's ability to produce and deliver chemical and biological weapons.

The plan - codenamed Desert Thunder - calls for four days of round-the-clock air assaults, which also will try to knock out Iraq's military infrastructure, the New York Times reported. One official, however, cautioned that additional "refinements" are always made to such preparations.

Berger denounced the Times report, calling it marred with errors but declining to elaborate. "Unlike the people who were discussing that with reporters, I'm not going to discuss operational details," he said.

While planners anticipate that a prospective air campaign most likely would generate only a handful of American casualties, as some planes fall to enemy fire, accidents or mechanical failure, there is risk from "friendly fire." In the 1991 Gulf War, 35 of the 148 Americans killed were lost in such incidents.

Planners also have been actively preparing for the possibility that Saddam could strike back with terrorist-style bombings targeting U.S. bases in the region, fire off Scuds missiles - possibly with nerve-gas or germ warheads - or even mount a desperate tank attack in the direction of Kuwait.