An advance team of U.N. inspectors arrived here this afternoon to resume the search for weapons of mass destruction in Iraq, a politically sensitive and logistically challenging mission that could determine whether the United States launches a war against President Saddam Hussein's government.

After arriving at Saddam International Airport aboard a civilian version of a C-130 Hercules cargo plane, Hans Blix, the chief U.N. inspector, said comprehensive and credible inspections are "in the interest of Iraq and the interest of the world."

Perhaps mindful of his surroundings and his desire for Iraqi cooperation, Blix struck a more conciliatory tone than he did upon leaving U.N. headquarters in New York on Friday, when he warned Iraq that he would not tolerate "cat and mouse" games. In brief comments to journalists gathered at the airport here, he reiterated that his team would be fair to Iraq, adding: "We will report objectively. We will do our job professionally."

U.N. officials said Blix's comments were intended to win the confidence of Iraqi officials. But his strategy to seek cooperation over confrontation has been criticized by some officials in the Bush administration, which wants Blix to swiftly embark on intrusive inspections and impose strict reporting requirements on the Iraqi government to test Hussein's willingness to comply with a new U.N. Security Council resolution. Should Iraq fail to comply, President Bush has said, "the United States will lead a coalition and disarm him."

Before mentioning the danger of war, however, Blix emphasized that compliance would result in the lifting of economically debilitating U.N. sanctions imposed on Iraq after its August 1990 invasion of Kuwait. He also asserted that the cooperation of Hussein's government could help set in motion a political process to eliminate weapons of mass destruction in other Middle Eastern nations.

Although Blix did not specify Israel, it is the only nation in the region known to be equipped with nuclear weapons, a crucial strategic advantage that has long galled Iraq and other Arab countries. In addition, Egypt, Syria, Iran and perhaps Libya, in addition to Iraq , have been cited by U.S. officials as countries in the region that possess or are trying to develop chemical weapons.

Had Iraq complied with a U.N. order to disarm after the Persian Gulf War in 1991, Blix said, "then 10 years of sanctions would have been unnecessary." He added: "Now there is a new opportunity, and we hope that opportunity will be well utilized so that we can get out of the sanctions, and in the long term have a zone free of weapons of mass destruction in the Middle East."

The inspectors' arrival coincided with increased activity in the northern swath of Iraq designated by the U.S. and British governments as a "no-fly" zone for Iraqi aircraft. The U.S. military said allied warplanes bombed Iraqi defense systems today after being fired on during routine patrols.

A White House spokesman, Scott McClellan, said the Iraqi antiaircraft fire "appears to be a violation" of the new U.N. resolution. Iraq considers such patrols a violation of its sovereignty and frequently shoots at them. The Foreign Ministry issued a statement today vowing not to cease its "resistance to aggression."

The statement accused the Bush administration of "evil" and of using the new resolution "as a cover to justify their aggressive acts against Iraq."

In the south, U.S. planes bombed three sites after Iraqi air defense units fired on them. The strikes hit an air defense communications facility near Tallil and a radar and communications site near Al Kut.

The U.N. resolution, which was unanimously approved Nov. 8, calls for inspectors to be given access to any person or place in Iraq -- including mosques, military bases and Hussein's palaces -- without having to seek permission or provide advance notice. The resolution also requires Iraq to permit its scientists and their families to be interviewed abroad, and it gives Hussein's government until Dec. 8 to provide a complete account of the status of its chemical, biological and nuclear facilities.

Full-scale inspections are to resume after the Iraqi declaration. Blix has been asked to deliver a report to the Security Council within 60 days.

Although his government has condemned the resolution as a violation of Iraq's sovereignty based on concocted evidence, Hussein accepted it last week amid warnings that it was a last-ditch chance to avert a U.S. attack. The resolution states that Iraq could face "serious consequences" if it fails to cooperate.

Izzat Ibrahim, vice chairman of Hussein's ruling Revolutionary Command Council, was quoted by the official Iraqi News Agency as saying Iraq had acceded to the U.N. resolution to protect its people from "American arrogance," but that it was prepared to fight "if war is imposed on us."

U.N. inspectors first arrived in Iraq in 1991, shortly after the war. They have been credited with destroying large quantities of its chemical weapons stockpile and monitoring equipment that could be used in the manufacture of nuclear and biological devices. But the inspectors found themselves embroiled in frequent disputes with the government, which restricted their ability to travel and visit certain sites. Finally, in 1998, the inspectors withdrew, declaring that Iraq's defiance prevented them from carrying out their work. The United States and Britain subsequently launched four days of airstrikes against Iraq.

Blix, a 74-year-old Swedish diplomat who used to head the International Atomic Energy Agency, was accompanied by Mohamed elBaradei, the IAEA's current director, and about 25 technical personnel who will set up communications systems, arrange transportation and assemble monitoring equipment for the inspectors.

About 12 arms experts are scheduled to arrive Nov. 25 and formally begin inspections two days later, according to Ewen Buchanan, the inspectors' chief spokesman. They will be joined by another 80 inspectors in the following weeks, he said.

Iraq contends some previous inspectors worked as spies for the United States and other Western nations, which at least one former senior inspector has confirmed. In that light, Blix was peppered with questions from Iraqi and other Arab journalists about whether he would accept intelligence from the United States.

"We will receive intelligence information from all over the world," Blix said. "The more diversified, the better."

The advance team was met at the airport by a delegation led by Gen. Hussam Mohammed Amin, director general of Iraq's national monitoring directorate, which was set up as a counterpart to U.N. inspection teams. This afternoon the team traveled to its former offices in a U.N. compound here, which have been sealed since 1998. Buchanan said the team brought five industrial-strength vacuum cleaners "to clean up four years of dust."

Chief U.N. weapons inspector Hans Blix arrives in Baghdad to begin inspections under the new Security Council resolution.Members of the advance team of U.N. weapons inspectors wait aboard a bus to be driven from the airport into Baghdad. They will work under the terms of the new Security Council resolution, approved Nov. 8, which orders Iraq to give them access to any person or place in the country.U.N. weapons inspector Hans Blix talks to reporters upon arrival at Saddam International Airport.