The top U.N. arms experts said tonight that they were unable to reach agreement with Saddam Hussein's government on several key issues they had traveled here to resolve in a bid to build support for continuing weapons inspections.

The two chief U.N. inspectors, Hans Blix and Mohamed ElBaradei, failed to achieve three top goals during two days of meetings with senior Iraqi officials: the disclosure of significant new evidence about Iraq's past weapons programs; safety guarantees from Iraq for reconnaissance aircraft to aid in inspections; and a high-level declaration criminalizing the production of nuclear, chemical or biological arms.

Blix sought to cast the talks in the most positive light possible by saying he saw the beginning of an Iraqi understanding that it must seriously observe U.N. demands for disarmament, but he acknowledged at a news conference this evening that he had not achieved a "breakthrough." Iraqi concessions on substantive issues, he said, were "less good" than he was expecting.

The results of the meetings could have a far-reaching impact on the diplomatic brawl at the United Nations over U.S. demands that the inspections cease and that military force to topple Hussein be approved by the Security Council. U.N. officials said the discussions will play a significant role in shaping a crucial progress report Blix plans to give the council on Friday, and lack of agreement likely will be seized upon by the Bush administration to reinforce its case that the inspections are not working.

White House spokesman Ari Fleischer, asked about Blix's statements, noted that the president has said: "Given the fact that Saddam Hussein is not disarming, time is running out."

In remarks delivered to congressional Republicans before Blix spoke today, President Bush said Hussein "wants the world to think that hide-and-seek is a game that we should play."

"It's over," Bush said. "It's a moment of truth for the United Nations. The United Nations gets to decide shortly whether or not it is going to be relevant in terms of keeping the peace, whether or not its words mean anything."

The inspectors did receive several documents that Iraqi officials said would answer long-standing questions about Iraq's past nuclear, biological and chemical weapons programs, specifically the production of anthrax bacteria and VX nerve gas, as well as the development of two rockets U.N. experts believe can exceed a 93-mile limit imposed on Iraqi missiles. But one U.N. official who saw the papers characterized them as "talking points" and not the sort of new evidence the inspectors had been seeking.

"They are welcomed," Blix said of the documents, "but they are not the answer."

Blix also said the issue of private interviews with Iraqi scientists now appeared to be a "mixed bag." Of the five non-nuclear scientists whom inspectors sought to interview in confidence since Thursday, only three agreed to do so without a government official present, U.N. sources said.

Despite the overall lack of progress, Blix and ElBaradei said they still held out hope that Iraq would relent on some of their key demands in coming days. A senior Iraqi official said tonight that his government hoped to reach a deal on the reconnaissance flights before Blix speaks to the council on Friday. The Iraqi government also said it would set up a commission to find and hand over documents wanted by the inspectors.

"I would say I'm beginning to see a change of heart on the part of Iraq," ElBaradei said.

In this weekend's meetings with Blix and ElBaradei, Iraqi officials for the first time stopped dismissing the contention that Iraq still has unresolved disarmament issues, a senior U.N. official said. "They finally acknowledged there were issues that needed to be resolved," the official said.

But ElBaradei, who heads the International Atomic Energy Agency, expressed frustration that Iraq still was not moving with enough alacrity to address those issues. "At this crucial time, at this critical time, we need 100 percent Iraqi cooperation," he said.

ElBaradei said he and Blix were mindful of the desire of the Security Council "to see quick progress," saying he told Iraqi officials that the world would "need to see . . . drastic change" in the coming days. "Something spectacular has to happen," he said.

The two-day visit, the second Blix and ElBaradei have made to Baghdad in a month, starkly illustrated the diplomatic tightrope both men must walk. While they are trying to prod Iraqi officials to be more cooperative, they fear that being overly critical will fuel U.S. efforts to pull the plug on the inspections. As a consequence, both men sought to nudge Iraq along, saying they hoped disarmament still could be achieved without a war.

"The ball is very much in Iraq's court," ElBaradei said. "If we see full cooperation . . . on all the issues, then I believe we will be given time we need. As long as we're registering good progress, I think the Security Council will continue to support the inspection process."

Saying they were hopeful Iraq would offer more concessions, Blix and ElBaradei called for a continuation of the inspections. "Inspection does work," ElBaradei said. "Inspections are making progress and, in fact, inspection is -- and can -- provide an alternative to war."

Asked about a statement by Bush that "the game was over" for Iraq, Blix said: "Well, we are still in the game."

Hussein's top adviser on weapons issues, Gen. Amir Saadi, expressed guarded optimism that Iraq's hand-over of documents and its promise to resolve the issue of reconnaissance flights would be welcomed in the Security Council. "We believe it should satisfy the skeptics and also satisfy the fair-minded," he said. "That's best we can do. If something else happens, we hope sanity will prevail."

The inspectors want guarantees from the Iraqis that they would not attempt to shoot down U-2 surveillance aircraft flying under U.N. orders and marked with U.N. insignia. Iraqi officials have insisted they cannot ensure the safety of the high-altitude planes if U.S. and British fighter jets do not cease patrols over portions of northern and southern Iraq designated as "no-fly" zones. Iraqi antiaircraft guns and missile batteries routinely target the U.S. and British planes, and officials here have warned that a U-2, even if it were flying under U.N. authority, could be mistaken for a warplane.

Saadi said Iraq was trying to work out a compromise with the United Nations that would involve the inclusion of non-U.S. aircraft, including French and Russian jets as well as unmanned German drones, in the reconnaissance patrols.

"We are confident we can reach some measure of success soon," Saadi said.

The inspectors said today that they had found another empty missile warhead equipped to carry chemical weapons at an ammunition depot north of Baghdad. Inspectors have identified 18 such warheads over the past few weeks, although none was loaded with chemical agents.

Chief U.N. arms inspectors Hans Blix, center, and Mohamed ElBaradei, right, said in Baghdad that Iraqi officials failed to turn over significant information on past nuclear, chemical or biological weapons programs.U.N. weapons inspectors in Baghdad take their investigation to the Badir al-Kubra elementary school as part of continuing efforts to uncover prohibited Iraqi weapons programs.Arms specialists carry equipment that they used to scan the playground area of the Badir al-Kubra elementary school.