U By Maggie Farley

NITED NATIONS – As 17 inspectors arrived in Baghdad on Monday to prepare for their first foray to suspected weapons sites in four years, their chief told the U.N. Security Council that they will assume Iraq has weapons of mass destruction unless it can prove otherwise.

The inspectors’ stance puts great pressure on Iraq, which maintains it has no such weapons, but must provide an inventory on Dec. 8 of anything that can be used to make biological, chemical or nuclear arms.

It also signals that when inspections actually begin Wednesday, the inspectors will take a tougher line than in the past, forcing Iraq to back up its assertions with “convincing evidence” such as documents or testimony – even if it has nothing to declare. The Security Council will likely regard intentional omissions and lack of cooperation with inspectors as a trigger for military action.

“The production of mustard gas is not exactly the same as production of marmalade. You do expect those who produce chemical weapons to keep some tracks of what they have produced,” Hans Blix, the chief weapons inspector, said after meeting with the Security Council. “They have provided a lot of figures to (inspectors) in the past. These figures do not give a full account. If they want to be believed, they had better provide either the weapons, if they remain, or better accounts.”

Blix, 74, said Iraq’s previous declarations under an inspection program that ended in 1998 left “open questions” about its weapons capabilities. The list of items that group of inspectors said was unaccounted for when they left includes 3,000 tons of precursor materials for biological weapons, 360 tons of chemical weapon agents, 30,000 munitions for delivery of weapons, VX nerve gas and 7,000 liters of anthrax.

The new inspectors arrived Monday aboard a white C-130 transport plane along with a cargo of high-tech sensors and computers they will use when they start their inspections later in the week. U.N. officials said that the first inspections will check on surveillance equipment left in place when the last group of inspectors pulled out.

The team will later look at new or rebuilt sites. Dozens more inspectors are scheduled to arrive Dec. 8 with a buildup to nearly 100 inspectors by Christmas.

At the United Nations, Blix warned of potential flashpoints: while Iraqi officials professed their intention to cooperate, they told him that “entry to ministries and presidential sites are not the same as entry to factories.”

But the Security Council resolution passed unanimously Nov. 8 authorizes U.N. inspectors to go anywhere at anytime – especially to those sensitive sites such as presidential sites that were previously protected by special arrangements. Blix said inspectors had re-established a 24-hour hot line with Iraqi officials to arrange surprise visits in the middle of the night, if they choose.

Iraqi officials still are confused about how to complete the declaration due Dec. 8, specifically about how to account for some materials used in petrochemical factories, medical labs and research centers, and the agricultural sector that might also be used to produce banned weapons. Iraq has hundreds, perhaps thousands, of such sites, and Iraqi officials are worried that “time for submission was short and omissions could have serious consequences,” Blix told the council.

Blix said he told Iraqi officials to focus on the weapons, and that inspectors could follow up with questions on dual-use goods later. But he also warned them to check their stocks and storerooms carefully for anything they might have overlooked before reporting a clean slate.

“They are aware that the consequences could be very serious,” he said.

Inspectors have learned lessons from Iraq’s past “full and final” declarations that turned out to be anything but. The previous team of inspectors found documents that detailed a biological weapons cache much greater than Iraq had reported. Iraq made several subsequent “final” reports.

With the threat of war hanging over the inspectors’ mission, this report really will be Iraq’s “final chance,” the Security Council has cautioned.

Those warnings were repeated by world leaders Monday after Iraqi Foreign Minister Naji Sabri sent an 11-page letter to Secretary-General Kofi Annan over the weekend with a point-by-point rebuttal of the Nov. 8 resolution.

Secretary of State Colin L. Powell, en route to Mexico City, told reporters that the letter “was certainly not indicative of a cooperative attitude.”

“We have no doubt he does have weapons of mass destruction,” British Prime Minister Tony Blair said of Iraqi President Saddam Hussein at a news conference in London. “But I have made it clear throughout that this has got to be a situation in which there is an honest declaration by Saddam.”

In Paris, Annan and French President Jacques Chirac urged Iraq to cooperate fully with the inspectors.

“It’s the only way to avoid a military conflict in the region,” Annan said.

Chirac urged Baghdad to offer the inspectors all they needed to do their job.

Against the backdrop of resumed inspections, Security Council members also haggled Monday over how long to extend a humanitarian program for Iraq and whether to add more items to a list of goods it may not import.

After the United States refused to renew the plan for the usual six months, the council agreed to extend the oil-for-food program, which expires at midnight, until Dec. 4 so negotiations between Washington and the other 14 nations could continue.

The plan allows Iraq to import food, medicine and other supplies to ease the impact of U.N. sanctions imposed after Saddam’s 1990 invasion of Kuwait. It allows Iraq to sell unlimited quantities of oil, with revenues going into a U.N. account that pays vendors of goods Iraq orders.

The United States, and particularly the Pentagon, wants to add items to the “goods review list” of civilian supplies going to Baghdad that could have military uses and must be reviewed separately by Security Council members.