Hans Blix, the man responsible for hunting down Iraqi President Saddam Hussein's weapons of mass destruction, remembers an incident that occurred during his first visit to Iraq four months after the Persian Gulf War ended that sums up the challenges his inspectors face every day.

He was driving through the desert with the head of the Iraqi Atomic Energy Commission to search for materials that could be used to make an atomic bomb. At one point, the Iraqi looked the veteran Swedish diplomat in the eye and told him: "Mr. Blix, we do not have a uranium enrichment program."

It was a blatant lie, which became obvious when U.N. inspectors discovered secret Iraqi blueprints for a weapon equivalent in size to "Little Boy," the U.S. atomic bomb that destroyed Hiroshima in 1945. The question is how the man who has now become the chief United Nations weapons inspector on Iraq -- whose investigations could determine whether there will be war or peace in the Middle East -- reacted to that lie.

To hear Blix tell the story, he used the incident to push for a more stringent inspection regime -- including access to undeclared nuclear sites previously off-limits to inspectors -- that has made it much more difficult for countries such as Iraq and North Korea to build a nuclear weapon. To listen to his critics, he was far too timid about challenging the claims of sovereign governments whose cooperation he needed to do his job.

A little-known international bureaucrat thrust into the limelight by the Bush administration's war on terrorism, Blix, 74, has become a flashpoint in a heated debate about the effectiveness of U.N. weapons inspections. Much of the controversy revolves around his record between 1981 and 1997 when he was head of the International Atomic Energy Agency (IAEA) with responsibility for combating the proliferation of nuclear weapons. It was the political springboard to his present post.

"Blix is the ideal man for the job," said John Ritch, who worked closely with the Swede as U.S. ambassador to the Vienna-based nuclear agency during the Clinton administration. "The Iraqis have to fear Blix precisely because he is very polite and very careful. If they hide anything, he will report it in a way that is accurate, judicious and ultimately very dangerous for the Iraqis."

Richard Perle, who is chairman of a Pentagon advisory body, said, "He was outwitted, outsmarted and outmaneuvered by Saddam Hussein." Perle voiced the the private criticisms of Defense Department hawks: "The relationship between the IAEA and countries like Iraq is far too cozy. . . . You have to be brain dead to assume that Saddam Hussein is not going to hide things."

There is another, competing version of Blix's journey into the Iraqi desert in May 1991 that encapsulates the views of critics who argue that he is too accommodating to stand up effectively to a ruthless and secretive regime bent on acquiring doomsday weapons. It comes from one of his former subordinates, an American nuclear inspector named David Kay, who was the third passenger in the car, sitting next to the driver.

All three men -- the Iraqi, the Swede and the American -- had taken a three-hour car ride to inspect a pile of garbage suspected of containing nuclear isotopes. The Iraqi expert said it was scientifically impossible to detect a uranium enrichment program by examining the trash. Kay disagreed, and they had an argument. By Kay's account, Blix later reprimanded him for contradicting "the government of a member state."

"I was flabbergasted," Kay said. "Blix has had a hard time learning that people who wear coats and ties can make baldfaced lies, and not be ashamed of doing it. The essence of dealing with the Iraqis is that they are perfectly happy to go from one lie to another. Blix has had a hard time accepting that."

Blix said Kay's version of the conversation is "totally ludicrous."

In a wide-ranging interview, Blix depicted himself as the servant of an international monitoring system that has been strengthened enormously over the past decade in response to violations by countries such as Iraq and North Korea. Until 1991, he said, it was politically infeasible to strengthen the inspection regime because of opposition from U.N. member states, including some Western countries. As a result of the Iraqi "debacle" -- the discovery that Hussein had a secret nuclear weapons program going back at least a decade -- everything changed.

Blix said that, after returning from Baghdad, he went to the IAEA's board of governors to demand much greater access to nuclear weapons sites and more intelligence sharing by member governments to back up the work of his inspectors. He was granted broader powers, which he was able to use effectively the following year, when the agency discovered that North Korea was separating plutonium in violation of international agreements. The North Korean plutonium program was subsequently frozen.

Blix's interest in nuclear issues dates to the 1970s when, as a leader of the small Swedish Liberal Party, he campaigned in favor of nuclear energy in a fiercely contested referendum. He served briefly as Swedish foreign minister. "He was obsessed with treaty law, the United Nations and laws governing . . . the use of weapons such as napalm," recalled Jan Eliasson, the current Swedish ambassador to Washington and a longtime colleague.

During the early part of Blix's tenure as head of the IAEA, Iraq was a member of the board of directors and, therefore, in a position to block an effective inspection regime. Inspectors were permitted to visit only declared nuclear sites, meaning that it was difficult to detect cheating by a country like Iraq, which took elaborate steps to hide its weapons program from international supervision.

"There were severe constraints" on what the atomic agency was allowed to inspect before 1991, Blix acknowledged. Even so, he noted, his agency was not the only organization that failed to detect signs of Iraq's secret nuclear weapons program. "Neither the CIA nor [the Israeli intelligence service] Mossad knew what was going on, and they were not as constrained as we were."

Blix's critics argue that he was too willing, on the basis of partial evidence, to give the Iraqis a clean bill of health. Indeed, throughout the 1980s, he went out of his way to praise the Baghdad government for its cooperation, and to emphasize that there was no evidence Iraq was trying to build a nuclear bomb.

By several accounts, Blix remained reluctant to criticize Iraq in the weeks immediately after the Persian Gulf War, when his inspectors began to suspect large-scale Iraqi cheating. According to Bill Nelson, an American scientist from the Lawrence Livermore National Laboratory who was a member of the first nuclear inspection team to visit Iraq after the war, the prevailing culture at the atomic agency was to assume that member governments were telling the truth until they were caught in a flagrant lie.

Blix had "a nonaggressive approach," said Rolf Ekeus, a fellow Swede who headed the United Nations Special Commission (UNSCOM), the first U.N. effort to find Iraqi weapons of mass destruction. According to Ekeus, Blix believed he was receiving "good cooperation" when the Iraqis permitted his inspectors to visit nuclear facilities and showed them documents. "For me, it is not cooperation if they have lied and haven't told you everything," Ekeus said. "We come from two different cultures."

Ekeus's former deputy, U.S. diplomat Robert Gallucci, recalls loud arguments in Swedish over how to deal with Hussein. Gallucci, who now heads the School of Foreign Service at Georgetown University, said he found Blix "entirely too sympathetic to the Iraqi position and Iraqi explanations" in the immediate aftermath of the war.

Nevertheless, Gallucci and others give Blix great credit for strengthening the mandate of the atomic energy agency once he received incontrovertible evidence that the Iraqis had been cheating. "It was a watershed moment," said Gallucci, referring to an IAEA board meeting in February 1992, when Blix argued persuasively for greater powers. "He brought the agency along with him."

Blix himself attributes his conflict with Ekeus mainly to bureaucratic turf issues. He says UNSCOM treated the nuclear agency like "a watchdog on a leash," telling it where it should go and inspect. At the same time, he concedes that he remains allergic to words such as "aggressive" in describing how his inspectors should operate in Iraq and prefers words such as "tough" and "dynamic."

"We can neither shoot nor should we need to shout. The power that we have at the present time is very considerable," he said. The Iraqis "know that we have a big stick. Everybody knows that."

As the former head of UNSCOM, Ekeus was the first choice of U.N. Secretary General Kofi Annan to head the United Nations Monitoring, Verification and Inspection Commission, or UNMOVIC, as the successor agency is known. But both the Russians and the French vetoed Ekeus's candidacy, believing he is too tough to be acceptable to the Iraqis. The French proposed Blix, instead.

When Annan called him with the news, Blix was hiking in southern Patagonia with his wife. It was January 2000. His initial instinct was to turn down the job, a friend said. Blix, who was 72 and retired, felt there was little chance of getting back into Baghdad, as the Iraqis were adamantly opposed to allowing the inspectors to return. But after thinking over Annan's offer, he agreed to accept it.

Blix sees the latest round of inspections as a chance to prove the effectiveness of the international monitoring system. He says UNMOVIC has several advantages over its predecessor, including a tougher U.N. mandate and greater independence. UNSCOM experts were on the payroll of U.N. member governments, including the United States. Blix's inspectors, by contrast, receive their salaries directly from UNMOVIC, which is funded out of confiscated Iraqi oil revenue.

A key issue for Blix's Pentagon critics will be how effectively he uses a provision in the U.N. resolution setting up UNMOVIC that permits him to take Iraqi scientists and their families outside the country if they have vital information on Hussein's secret weapons programs. Blix has raised practical objections to a large-scale defector program, saying that the inspectors are not running "an abduction agency" and cannot force scientists to leave Iraq.

Pentagon officials, by contrast, believe that defectors are likely to provide the key to tracking down Iraqi weapons of mass destruction. The "reality" of inspections, Defense Secretary Donald H. Rumsfeld told reporters Tuesday, is that "things have been found [in Iraq] not by discovery, but through defectors."

White House officials, meanwhile, are still expressing confidence in Blix. "We believe Dr. Blix is a man of integrity with a very difficult job," said National Security Council spokesman Sean McCormack.

Blix said "it is vitally important that we do not overstate what can be achieved by inspections." He conceded it will be "very difficult" to find convincing evidence of Iraqi biological and chemical weapons programs in the absence of "extremely fresh intelligence." At the same time, he noted that the alternative to inspections is war and the deaths of thousands of people.

For the moment, even the harshest critics seem to be willing to allow Blix to continue with his inspections. "We are giving Saddam Hussein a last chance," said Perle, the unofficial spokesman for Pentagon hawks. "We should be willing to give Hans Blix a last chance as well."

Hans Blix's record is a key part of a debate about the value of U.N. weapons inspections. Even the harshest critics of chief U.N. weapons inspector Hans Blix seem willing to let him continue his work in Iraq.Hans Blix, then-head of the International Atomic Energy Agency, talks to reporters in Beijing after a 1992 visit to North Korea. He now says that his earlier work for the IAEA in Iraq led to a more stringent inspection regime.Blix, right, confers in Baghdad with Lt. Gen. Hussam Amin of the Iraqi National Monitoring System. He views the latest round of inspections as a chance to prove the effectiveness of the international monitoring system.