With an advance team of U.N. weapons inspectors due to arrive in Baghdad on Monday after a four-year absence, the United States and the United Nations are divided over how aggressively the inspectors should conduct their hunt for chemical, biological and nuclear weapons programs in Iraq, U.N. and U.S. officials say.

The Bush administration is insisting on the most intrusive inspections possible, pushing U.N. arms experts to probe where previous inspectors could not, and to impose strict reporting requirements on the Iraqi government. Secretary of State Colin L. Powell cautioned Thursday against the view that Iraqi President Saddam Hussein will be given any "slack" in the inspection process that would deter the United States from using force if Iraq fails to cooperate.

The U.N.'s chief weapons inspector, Hans Blix, has argued for a more measured approach to achieving disarmament. Blix spelled out his aims last month in Vienna at a meeting with recruits to the inspections teams; he said they should be "firm" with their Iraqi counterparts but never "angry and aggressive."

The division reflects broad differences in the U.N. Security Council that remain unresolved despite the council's unanimous approval Nov. 8 of Resolution 1441, which sets out stringent new terms for inspections in Iraq. And it may foreshadow clashes between the United States and its partners in the United Nations as Blix and his teams begin their inspections Nov. 27.

In a letter today to Iraq's parliament explaining why he accepted the resumption of inspections, Hussein reiterated his contention that Iraq is "devoid of weapons of mass destruction."

The claim was dismissed by President Bush in his weekly radio address. "We have heard such pledges before, and they have been unfortunately betrayed," Bush said. "Our goal is not merely the return of inspectors to Iraq; our goal is the disarmament of Iraq. The dictator of Iraq will give up his weapons of mass destruction, or the United States will lead a coalition and disarm him."

While Bush has argued that the 15-nation Security Council should have "zero tolerance," making even minor infractions a potential cause for military action, Blix, U.N. Secretary-General Kofi Annan and other key Security Council members, such as Russia and France, maintain that Iraq will be held accountable only for serious violations

"The U.S. does seem . . . to have a lower threshold than others may have" to justify military action, Annan told reporters in Washington on Wednesday before meeting with Bush. "I think the discussion in the council made it clear we should be looking for something serious and meaningful, and not for excuses to do something."

Annan's view reflects those of U.N. members who have interpreted comments by senior White House and Pentagon officials as suggesting that conflict with Iraq may be inevitable.

Since the Security Council vote, administration officials have argued that the resolution prohibits Iraq from firing on U.S. and British warplanes enforcing "no fly" zones over northern and southern Iraq. The resolution says Iraq shall not take or threaten hostile acts against U.N. member personnel upholding "any" previous resolutions, but the United States has differed with other U.N. members over whether the Security Council ever sanctioned the "no fly" zone policy.

Asked about the matter in Canada on Thursday, Powell acknowledged that "one could argue" with the U.S. interpretation. But he said the United Nations was seeking a "new spirit of cooperation" from Iraq, and that, therefore, firing on aircraft would suggest Iraq's behavior had not changed. "If they were to take hostile acts against United States or United Kingdom aircraft patrolling in the 'no fly' zones, then I think we would have to look at that with great seriousness," Powell said.

The issue was thrust into the open today as administration officials said they have determined that an attack by Iraqi air defenses Friday against U.S. and British warplanes patrolling a "no fly" zone in southern Iraq was a "material breach" of Baghdad's obligations under the terms of the resolution. The Iraqi government said that seven civilians were killed and four injured by allied planes responding to the attack.

Blix and Mohamed El Baradei, director general of the International Atomic Energy Agency, will arrive in Baghdad on Monday with more than 25 technical specialists. Blix told reporters Friday that he and El Baradei will meet with senior Iraqi officials while their team tends to communication and transportation. About 12 arms experts are to arrive Nov. 27 and formally begin the inspections. They will be joined by another 80 inspectors in the following weeks.

U.N. officials have voiced concern that the United States will press for the kind of provocative inspections that characterized the 1991-98 disarmament effort by the U.N. Special Commission, known as UNSCOM.

Blix, who assumed leadership of UNSCOM's successor agency in 2000, is trying to change the culture of the arms inspectors, whose predecessors aroused deep animosity in Iraq for using tough tactics to gain access to U.N. sites.

The conduct and composition of the inspections teams have emerged as a major issue. Iraq and other Arab governments appealed to Blix, who has employed more inspectors from the United States than from any other country, to hire more Arab arms experts, who might be more in tune with Iraq's religious and cultural sensitivities.

Iraqi Foreign Minister Naji Sabri made it clear in a letter to Annan on Wednesday in which Iraq accepted the resolution that his government will be monitoring the inspectors for evidence that they are spying on behalf of the United States.

"The fieldwork and the implementation will be the deciding factors as to whether the true intent was for the Security Council to ascertain that Iraq is free of those alleged weapons or whether the entire matter is nothing more than an evil cover" for U.S. aggression, Sabri wrote.

UNSCOM, which was established at the end of the Persian Gulf War in 1991 to eliminate Iraq's chemical, biological and nuclear weapons and missiles with ranges longer than 90 miles, is credited with destroying more Iraqi weapons than U.S.-led forces during the conflict. But it was shuttered in late 1999, following revelations that the United States had used the inspection agency to collect intelligence on the Iraqi government.

The Security Council established a successor agency, the U.N. Monitoring, Verification and Inspection Commission, or UNMOVIC, in December 1999 to complete Iraq's disarmament. The new inspectors have been placed on the U.N. payroll to decrease the likelihood that they will serve the interests of their governments.

Iraq refused to allow the new inspection agency to resume its work, however, until it was confronted by a credible threat of U.S. military action.

The United States has pressed Blix to appoint a senior U.S. official to manage the flow of American intelligence to the inspection agency. It has also insisted that Iraq be required to permit its scientists and their families to be interviewed abroad, and imposed a 30-day deadline on Iraq to provide a complete account of the status of its chemical, biological and nuclear facilities.

Blix has not yet agreed to the U.S. request about having an American in charge of monitoring the intelligence flow. Although Blix has pleaded with Washington to increase its intelligence support for UNMOVIC, he has also expressed concern that the relationship could compromise his organization. He said today in Paris that the former inspection agency had "lost its legitimacy by being too closely associated with intelligence and with Western states."

Speaking to reporters Friday before leaving New York, Blix said there may be "practical difficulties" in conducting interviews outside Iraq. He also has questioned whether Iraq could file a full declaration on its petrochemical industry within the 30-day deadline, making it clear that he would judge Iraq's "intention" before deciding whether Iraq has violated any of the resolution's requirements.

Some former weapons inspectors say they are concerned Blix may be falling into an Iraqi trap and have urged him to undertake an even more aggressive approach to inspections than UNSCOM. "Blix may go too far down this line," said David Albright, a former nuclear inspector who heads the Institute for Science and International Studies. "If you are too weak, the Iraqis will read you in a second and take advantage of it."

Ewan Buchanan, right, of the U.N. Monitoring, Verifications and Inspections Commission (UNMOVIC) is in Larnaca, Cyprus, with an advance crew.