The two chief U.N. weapons inspectors arrived here today to urge Saddam Hussein's government to turn over evidence about Iraq's arms programs and accede to overflights and other demands.

The chief inspectors, Hans Blix and Mohamed ElBaradei, have suggested that if Iraq does not make significant concessions, they will probably deliver a fairly negative assessment of Iraqi cooperation to the U.N. Security Council on Friday. Diplomats have said a highly critical report could encourage France, Russia and China, which wield veto power on the council, to support U.S. demands for a resolution authorizing war against Iraq instead of insisting that inspections be allowed to continue.

"It's not midnight, but it's closing in on midnight," said a U.N. official traveling with the delegation.

U.N. and Iraqi officials offered few details about today's meetings, but a senior U.N. source said Iraq provided additional documents to Blix and ElBaradei this evening. The source said the documents needed to be studied but would not specify the quantity or the contents.

Blix and ElBaradei held meetings at the Foreign Ministry this afternoon, and more talks are planned for Sunday. The inspectors are expected to reveal at a news conference Sunday night what progress, if any, they have made.

"It is useful discussions we are having," Blix said as he left the Foreign Ministry after more than three hours of talks. "It was a very substantial discussion."

ElBaradei said that "the Iraqi side is providing explanations on some of the issues. We have to see the results tomorrow."

But a senior U.N. official said "it's not enough" for Iraq to allow the U-2 reconnaissance flights over the country as requested "or give us two or three scientists in private interviews." "They really have to come up with substantive evidence," the official said.

Even if the inspectors receive the responses they are seeking, that might not sway the Bush administration against military action. The United States has deployed more than 100,000 troops within striking distance of Iraq and is sending more. On Thursday, President Bush warned that last-minute concessions by Iraq would not prevent war, saying, "the game is over." And in Munich today, Defense Secretary Donald H. Rumsfeld said that "diplomacy has been exhausted, almost" and warned key U.S. allies, particularly France and Germany, that their reluctance to support a military strike was threatening the integrity of NATO and the United Nations.

The U.N. inspectors want Iraq to relent on procedural and substantive issues. On the procedural side, they seek guarantees that the Iraqis would not try to shoot down U.N.-marked U-2 aircraft. Blix and ElBaradei also want Iraq to enact legislation criminalizing the production of weapons of mass destruction.

Iraqi officials have insisted they cannot guarantee the safety of high-altitude surveillance planes flying on the inspectors' orders if U.S. and British fighter jets continue patrols over portions of northern and southern Iraq designated as "no-fly" zones. Iraqi officials, who do not recognize the zones, have ordered antiaircraft guns and missile batteries to target the planes.

In the mid-1990s, Iraq provided safety assurances for the inspectors' U-2s despite the U.S. and British patrols, if a flight plan was submitted to the government in advance. Blix has offered to furnish flight plans and suggested a possible path to agreement in the meetings here.

U.N. officials acknowledge that legislation on weapons of mass destruction would have little immediate impact but said they want Hussein's government to make a firm statement condemning them and encouraging people to cooperate with the inspectors.

After weeks of pressure, Iraq relented on another key procedural issue Thursday: private interviews with scientists. Although the Nov. 8 Security Council resolution authorizing the latest round of inspections required Iraq to provide "private access" to anyone the inspectors wanted to interview, when the inspectors asked to conduct confidential interviews, the scientists they approached insisted on having a government minder present.

Iraqi officials said the scientists were worried that their testimony would be mischaracterized. But U.N. and U.S. officials contended that Hussein's government prevented scientists from speaking out of fear they might spill secrets about banned weapons programs.

On Thursday, however, an Iraqi biologist acquiesced to a private interview. Inspectors conducted three more interviews Friday without minders present. A senior Iraqi official said the scientists had changed their minds because of the "circumstances that are now prevalent."

U.N. officials traveling with Blix and ElBaradei said Iraqi concessions on substantive issues pertaining to disarmament were even more important than the procedural agreements. Of greatest importance to the inspectors, the officials said, is a thorough accounting of Iraq's past weapons programs and evidence to support Iraq's claims that it destroyed tons of biological and chemical warfare agents it acknowledged producing before the 1991 Persian Gulf War.

In a series of declarations in the 1990s, Iraq acknowledged making three types of biological weapons, including about 2,245 gallons of anthrax bacteria. Iraq also admitted that it had developed nearly four tons of VX and 100 to 150 tons of sarin, both highly lethal nerve agents. But inspectors could not verify claims by Hussein's government that it had destroyed everything it manufactured.

"If they don't have the orders, if they don't have the paper, give us the people who were involved to talk to," another U.N. official said.