Digging into Iraqi computers, surveying scenes with detectives' eyes, U.N. specialists finally got down to the business of weapons inspection Wednesday at the start of a demanding, months-long job that could make or break peace in the Mideast. The inspectors revisited an Iraqi missile testing site, a nearby graphite rod factory, and a motor plant potentially linked to nuclear activities. They sounded satisfied with Iraqi attitudes.

"We hope the Iraqi response today represents the future pattern of cooperation," said Jacques Baute, the nuclear inspectors' leader.

The Iraqi side also sounded a businesslike note. "We opened doors and submitted to inspection openly," said Ali Jassam Hussein, director of the missile site 25 miles southwest of Baghdad along the Euphrates River.

The U.N. teams did not immediately disclose any significant new findings from their surprise inspections, and may never do so. In the volatile atmosphere surrounding Iraq, the inspectors are expected to leave it to their New York and Vienna agency chiefs to reveal serious problems in the campaign to strip Iraq of any capability in chemical, biological or nuclear weapons.

Those tensions sharpened on the inspectors' first working day Wednesday when an air-raid siren wailed in Baghdad, and Iraqi officials said a "hostile flight" had flown over the capital. The U.S. military, whose warplanes have routinely patrolled Iraqi airspace since the 1991 Gulf War, had no comment.

The United States has warned it will disarm Iraq by force if the inspections fail, with or without international help. Most other governments say only the U.N. Security Council can authorize such a move.

The U.N. teams will continue their field missions - difficult, detailed inspections of hundreds of sites - every day. They've resumed under a Security Council mandate after a four-year break, to assess whether Baghdad is still making to chemical, biological and nuclear weapons.

In New York, Norway's U.N. Ambassador Ole Peter Kolby, who chairs the Security Council committee monitoring sanctions against Iraq, said it appeared the first day's inspections went well.

"I think that was very positive," he said. "It looks to me as so far so good - that they carried out inspections. That's what we all hoped for. Soon there will be more inspectors, and then they will carry on and we'll see."

Syria's deputy U.N. ambassador Fayssal Mekdad, whose country is the only Arab nation on the 15-member council, also was upbeat.

"As we have always expected, the Iraqis have given all support, all cooperation, and we hope this will continue and the voices of war will go down in comparison with the very, very positive inspection that is going on now," Mekdad said.

Hans Blix, the chief weapons inspector, concurred that Wednesday's initial inspections went well. But he told CNN in an interview that it was up to Iraq to show it has no weapons of mass destruction.

"We maintain that the burden of proof is on Iraq," Blix said. "They object and say that anyone who is arraigned before a tribunal is acquitted if the prosecutor cannot prove the case.

"We say you are not in a criminal tribunal; you are in a situation where you want to create confidence that Iraq doesn't have any anthrax or anything else that's prohibited. That takes more than there's no evidence of it."

In one of Wednesday's three inspections, six white U.N. vehicles led journalists on a circuitous route to confuse Iraqi officials about their destination. The trip ended here among riverside wheat fields, outside the gates of a military-run graphite plant.

They gained immediate entrance, but most soon left and drove around back, to another sprawling compound - the al-Rafah testing station, where the Iraqis have long tried out engines for missiles, on skeletal steel structures called test stands.

U.S. intelligence analysts say satellite photos suggest that a new al-Rafah stand for holding and testing engines might be used for missiles larger than U.N. resolutions allow. Iraq is forbidden to develop missiles over 90 miles in range.

The Iraqis say the structure can be used only for the permitted shorter-range missile engines.

The inspectors spent five hours in the compound. Over the 7-foot-high walls surrounding the complex, journalists saw U.N. specialists crisscrossing the open testing area, wearing U.N.-blue baseball caps, clipboards in hand, packs on their backs.

They spent considerable time in a small concrete building that appeared to be a control center.

They also checked files and photographed documents, said director Hussein, a military engineer.

"They didn't find anything because we don't have anything illegal," Hussein told reporters, who were allowed limited access to the compound after the inspectors left.

The U.N. team leader, Demetrius Perricos, later told reporters his inspectors also went through the Rafah staff's computer files to try to understand the site's capabilities. Now, he said, "it has to be assessed."

Other inspectors surveyed the graphite plant next door. Perricos said the Iraqis noted graphite is used for "pencils and batteries," but he pointed out that it is also useful in the missile field - to lubricate nose cones, for example, for atmospheric re-entry. Again, the inspectors did not discuss their findings publicly.

Ten inspectors went to Wednesday's third site, al-Tahadi, a government factory just east of Baghdad that Iraqi officials said produces motors for cement factories, refineries and water pumping stations. The inspectors were staff members of the Vienna-based International Atomic Energy Agency, but factory director Haitham Maamoud said the facility never was involved in a nuclear program.

Baute would not discuss any findings. "I will first report to the (agency) director general," he said.

The three sites were visited by U.N. experts in the 1990s. Over seven years of work that ended in 1998, those inspectors destroyed large amounts of chemical and biological armaments and longer-range missiles prohibited under U.N. resolutions after the Gulf War. The inspectors also dismantled Iraq's nuclear weapons program before it could build a bomb.

The earlier inspections were suspended in 1998 amid disputes over U.N. access to Iraqi sites and Iraqi complaints of American spying via the U.N. operation.

In the new round, the inspectors are to report to the Security Council by late January on what they have found and Iraqi cooperation.

If the inspectors certify that Iraq has cooperated fully with their disarmament work, U.N. resolutions call for the lifting of international economic sanctions imposed on Iraq after it invaded Kuwait in 1990. If the Iraqis fail to cooperate, the council may debate military action against the Baghdad government

PHOTO CAPTION

Iraqis work at a military installation in the northeastern Baghdad suburb of al-Rashad Wednesday Nov. 27, 2002. The site, known as 'Just Defiance', was the first to be visited by UN inspectors with the resumption of inspections in Iraq Wednesday, following a four-year break. (AP Photo/Karim Sahib, POOL)