By BARBARA CROSSETTE

NITED NATIONS, Jan. 26 -- Hans Blix, a former director of the International Atomic Energy Agency, was chosen unanimously today by the Security Council to be the chief inspector of a new disarmament commission for Iraq.

Secretary General Kofi Annan said he would take the council's advice and appoint Mr. Blix, a Swedish lawyer who has attracted criticism for what some disarmament experts saw as a weak approach to nuclear inspections in his 16 years at the agency.

"He's a very experienced man, and I'm sure he knows what he's getting into," Mr. Annan told reporters after attending a council meeting on Congo. "I hope Iraq will cooperate."

Last week, Mr. Annan nominated Rolf Ekeus, another Swedish disarmament expert supported by the United States, to the chief inspector's job. But his nomination was blocked in the council by France, Russia and, to some extent, China.

The council president this month, Richard C. Holbrooke, the United States representative, coupled the announcement about Mr. Blix with a warning to President Saddam Hussein of Iraq not to try to obstruct the panel, the United Nations Monitoring, Verification and Inspection Commission. Iraq successfully hid a nuclear-weapons program from the atomic agency for more than a decade.

"The Iraqis understand this resolution," Mr. Holbrooke said, noting the council's unity after months of division and disarray. "They understand the continuing consequences if they obstruct this process. I think they are playing a very dangerous and, ultimately, self-damaging role if they continue to obstruct. Let's see what Baghdad does. Let's hope that they have some residual sense."

Mr. Holbrooke said the council had found consensus only over Mr. Blix. And it appears that France took the lead in resurrecting his name. Mr. Blix had been mentioned weeks ago as a possible compromise candidate, but faded from the competition. Mr. Holbrooke said his name just "came up out of the woodwork" on Tuesday and rallied the council in record time.

Mr. Blix, 71, was traveling in Antarctica today. He told United Nations officials that he would hold a news conference in Sweden early next month, when he returns.

He is not considered the strongest of more than 20 candidates who were in the running. But the United States was unwilling or unable to fight for a stronger nominee.

In the last two years, the intensity of American pressure in the council on Iraq issues has declined considerably, as the Clinton administration has turned its attention to efforts to replace Mr. Hussein. In Mr. Blix, they could agree to a respectable, experienced candidate, if not one likely to be confrontational with the Iraqis.

Under the cease-fire resolution that ended the war in the Persian Gulf in 1991, Iraq has to be certified free of all prohibited weapons systems and the means to reconstruct them before sanctions imposed in August 1990, after the Iraqi invasion of Kuwait, can be lifted.

Since last month, however, Iraq has enjoyed a much more liberal program of oil sales to pay for civilian goods. It is no longer limited on how much oil it can sell, a move that the United States did not oppose.

Some diplomats have questioned whether easing the sanctions will reduce the incentive to comply with resumed arms inspections, which the Iraqis flatly oppose. Today, the Iraqi representative to the United Nations, Saeed Hassan, repeated the objection, saying, "We are not dealing with this resolution."

Mr. Holbrooke praised Mr. Blix's appointment. "As the American representative, let me make clear that we are pleased with his nomination," he said. "We think he is an excellent choice."

From 1981 to 1997, Mr. Blix was director general of the atomic agency, based in Vienna. He saw the organization through some of its most difficult years. Critics said Mr. Blix's strong support for nuclear energy had led to a willingness to condone unsafe programs or extensive and loosely monitored projects in countries suspected of diverting peaceful research to secret work on weapons.

He came under his strongest attack when it was learned after the gulf war that Iraq had developed a secret nuclear-weapons program that the atomic agency had not detected in its routine inspections of Iraqi sites.

Paul Leventhal, president of the Nuclear Control Institute, a research organization in Washington, reflected the view of the critics when he said that under Mr. Blix's leadership the agency was always known as a somewhat timid watchdog.

"The willingness of the I.A.E.A. to give Iraq the benefit of the doubt when it could not come up with specific evidence to contradict Iraq's claims, that gives me real concerns as to how strong a chief inspector he can be," Mr. Leventhal said. "The big question about Blix is whether he has the backbone to stand up to the Security Council with findings that certain members of the council may not want to hear. I believe his track record at the I.A.E.A. suggests that he tends to bend to political will rather than come up with independent findings.

"This whole thing could become a farce. If the approach of the I.A.E.A. is now going to guide the new commission, I think the world will have to be highly skeptical about the kind of conclusions this commission reaches."

Supporters of Mr. Blix say pinning the blame for missing the Iraqi weapons programs on Mr. Blix is unfair.

"To criticize Hans Blix for Saddam's secret nuclear program is scapegoating," said John Ritch, the United States ambassador to the agency in Vienna. "Ten years ago, the I.A.E.A. could only monitor known nuclear facilities. And neither the U.S. or any other country was asking it to do more. These limited inspection powers left a window open for heavily disguised nuclear activity, and Saddam tried to walk through it.

"Blix was burned. But what he did after the gulf war is what counts. The I.A.E.A. dismantled Iraq's nuclear program. It detected and confronted North Korea for its nuclear violations. And with Blix's help, the I.A.E.A. acquired sweeping new inspection authority and investigative technologies, which are not being put into effect worldwide."

In 1995, the international board of governors, made up of member nations, gave the agency new powers to demand access to suspect sites for unannounced inspections and to sample soil, vegetation, water and air for traces of radioactivity. In 1994, Mr. Blix was involved in drafting an accord to roll back North Korea's illegal nuclear weapons program. Iraq and North Korea were violating the 1968 nonproliferation treaty.