Chief U.N. weapons inspector Hans Blix, preparing to make another crucial written report to the Security Council on March 7, told Iraqi representatives last week they must quickly provide detailed documentary evidence or witnesses to substantiate Baghdad's claims that it destroyed its former chemical and biological weapons and has no current program in those areas, according to senior U.N. officials.

Blix's reply to a request from Baghdad last week on what could be done to clarify the present situation was a tough message that the Iraqis "show a change of heart" and deliver "either hardware or documents or people," one U.N. official said.

Having ordered the destruction of Iraq's Al Samoud 2 missiles and associated items to begin by March 1, Blix is expected to include Iraqi President Saddam Hussein's response in his quarterly report to the Security Council.

One senior U.N. official said yesterday he was not surprised there was no immediate official reaction from Baghdad to the missile destruction order, because Blix had already told the Iraqis that "we are not going to discuss it." The only matter to discuss would be arrangements for inspectors from the U.N. Monitoring, Verification and Inspection Commission (UNMOVIC) to supervise the destruction.

While some U.N. officials believe a move by Iraq to comply with the missile destruction order would be a significant disarmament step and give support to those seeking to continue inspections, the United States plans to introduce a new U.N. resolution this week that would simply say Hussein has not disarmed and does not intend to.

President Bush yesterday called the Al Samoud 2 missiles "just the tip of the iceberg." And he added that even if Hussein destroys "however many he's going to destroy, [that] says to me that he's got a lot more weapons to destroy and why hasn't he destroyed them yet."

Meanwhile, Blix is preparing what he realizes could become a final work program based on key remaining disarmament tasks facing his UNMOVIC inspectors, who work on missiles along with chemical and biological weapons. Inspectors in the nuclear area, under Mohamed ElBaradei, director general of the International Atomic Energy Agency (IAEA), do not file such a report.

The UNMOVIC staff is preparing a list of unresolved questions going back to earlier inspections in about 30 disarmament areas, such as unaccounted-for VX poison gas, anthrax materials and 6,500 bombs, rockets and missile warheads that were declared in 1991 but whose alleged destruction has never been adequately substantiated.

The staff list of questions will be discussed Monday and Tuesday with UNMOVIC's 16 commissioners, who serve as Blix's advisory board. The board includes representatives of key countries in the current struggle over how long inspections should proceed -- the United States, France, Russia, Britain, Germany and China.

The final disarmament program may be included as part of Blix's written March 1 report, which is required under the U.N. resolution that set up UNMOVIC in 1999. Blix could report that one earlier question of Iraqi cooperation, permitting U-2 surveillance flights, has been satisfactorily resolved, but permitting interviews without the presence of Iraqi minders or tape recordings has not.

Bigger questions on cooperation in delivering substantial information remain.For example, according to the senior U.N. official, the Iraqis, who until last week had not been forthcoming with the names of individuals who could verify the destruction in the early 1990s of chemical and biological weapons, suddenly said they would produce a list of names and the specific destruction each person witnessed.

The Iraqis were then asked, one U.N. official said, that if they could produce such a list and people with such details, why wasn't there any written documentation to accompany such specific data?

In contrast to the search for information on chemical and biological weapons, the Al Samoud 2 data were provided by the Iraqis themselves in their Dec. 7 declaration. In it, they provided data on the missile and its engine size. Previous U.N. inspectors had tentatively concluded, as Blix has done, that the weapon has exceeded the 150-kilometer range limit imposed by U.N. resolutions. "They [the Iraqis] thought they could talk us out of it," one UNMOVIC official said last week.

In January and earlier this month, UNMOVIC experts discussed the missile with Iraqi specialists in Baghdad. Information from those discussions, findings by weapons inspectors in Iraq and four separate computer simulations of the ranges of the missile by experts from four countries were given to an expert panel. On Feb. 13, the panel unanimously concluded the missile was proscribed by sanctions imposed on Iraq after the 1991 Persian Gulf War.

Although no date has been officially set for Blix to discuss his quarterly report before the Security Council, a time has tentatively been set for March 7, which may make it central to the new U.S.-British resolution. Bush said yesterday that he expects Blix would be heard as part of the debate on the resolution.

Shown in a television interview earlier this month, U.N. chief weapons inspector Hans Blix is scheduled to submit his next Security Council report on March 7.