WASHINGTON, Dec. 19 — President Bush and Prime Minister Tony Blair of Britain announced Friday that Libya's leader, Col. Muammar el-Qaddafi, had agreed to give up all of his nuclear, chemical and biological weapons, a step Mr. Bush said could allow Libya to "regain a secure and respected place" among nations.

Libya's actions came after nine months of secret diplomacy, beginning with an overture from Colonel Qaddafi to London and Washington just as the invasion of Iraq was beginning.

Mr. Bush's aides, clearly seeking to build on the capture of Saddam Hussein last Saturday, described the Libyan action as directly linked to the Iraq war, suggesting that Colonel Qaddafi had decided to give up his weapons aspirations rather than face off against the United States and its allies.

Speaking to reporters in a hastily called session in the White House press room, Mr. Bush praised Colonel Qaddafi's agreement to open his country to full inspections.

This is the first time Colonel Qaddafi has admitted to having such unconventional weapons or programs to produce them, government and independent experts say.

But the details given by the White House indicated that for more than two decades, Libya had deceived international nuclear inspectors who have visited the country.

Like Iran, it hid facilities to produce nuclear fuel, though it did not appear that the Libyans actually succeeded in making the kind of fissile material needed to produce a bomb.

"Because Libya has a troubled history with America and Britain, we will be vigilant in ensuring its government lives up to all its responsibilities," Mr. Bush said.

His announcement came just two days before the 15th anniversary of the bombing of Pan Am 103, an act of terrorism for which a Libyan agent was convicted two years ago.

In a clear reference to North Korea and Iran, two other countries that are suspected of pursuing programs to develop unconventional weapons, Mr. Bush added that "I hope other leaders will find an example" in Libya's action.
In two trips to Libya, including one earlier this month, American and British intelligence and weapons experts were given a tour of the country's arsenal, reportedly including mustard gas, a World War I-vintage chemical weapon, and materials for making nerve gas and missiles, the latter from North Korea. None of these discoveries surprised the experts.

But one senior Administration official told reporters on Friday evening that the Libyans had gotten "much further" in their nuclear program than the United States had suspected, showing the Western visitors centrifuges that could be used to produce highly enriched uranium.

The officials declined to say what kind of centrifuges had been found, or what nations appeared to have helped Libya. Both North Korea and Iran have similar programs under way, though the administration official said that in Libya's case, Colonel Qaddafi's government had not declared that it had actually produced any weapons-grade uranium. "That is something we will be pursuing," the official said. He added that the United States had learned a considerable amount about North Korea's missile trading business in the course of the talks with Libya.

A British official said the Libyans had shown visitors 10 nuclear-related sites, adding that while the country had not manufactured a nuclear weapon, "it was close to producing one."

Inspectors from the International Atomic Energy Agency will be sent to assess how close, and to monitor the dismantling of the facilities, British and American officials said.

Not surprisingly, the White House described the surprise announcement as a victory for Mr. Bush in facing down rogue states developing such weapons. They also touted the Libyan move as vindication for the decision to go to war against Iraq — where no unconentional weapons have been found — because of the message it sent.

"In word and action, we have clarified the choices left to potential adversaries," Mr. Bush told reporters. "And when leaders make the wise and responsible choice, when they renounce terror and weapons of mass destruction, as Colonel Qaddafi has now done, they serve the interest of their own people and they add to the security of all nations." The Libyan government, in a statement, said it had made the decision of its own "free will."

The White House said that despite Libya's apparent renunciation of unconventional weapons, Mr. Bush was not yet ready to lift American sanctions; United Nations sanctions were removed on Sept. 12 after a settlement involving the Pan Am 103 bombing over Lockerbie, Scotland, which killed 269 people.

In London, Mr. Blair said the Libyan overture on disarmament was a direct outgrowth of the talks that led to the settlements over the bombing. Under that agreement, Libya agreed to pay at least $5 million to the relatives of each victim.

In January 2001, a Libyan military intelligence official was convicted in the bombing, while an executive with the country's airline was acquitted. Mr. Blair said Libya wanted "to see if it could resolve its weapons of mass destruction issue in a similarly cooperative manner."

Libya's latest actions complicate the debate over the Iraq war for the Democrats, particularly for Howard Dean, the apparent frontrunner in the primaries, who has opposed the war and said recently that the capture of Mr. Hussein had not made Americans any safer.

On Friday evening, though, many Democrats were calling Libya's renunciation of its weapons systems significant.
Ashton B. Carter, an assistant secretary of defense under President Clinton who is now co-director of the Harvard-Stanford Preventive Defense Project, agreed that Iraq was a turning point in convincing Colonel Qaddafi to give up his weapons.

"One certainly hopes that what we did in Iraq put countries like Libya on notice that we're really serious about countering proliferation," said Mr. Carter, who has been advising Dr. Dean.

Some families of those killed on the Pan Am flight, now preparing to mark the grim anniversary, were clearly taken by surprise by Mr. Bush's suggestion that relations with Libya could markedly improve.

"I am in a state of horror and sickened shock," said Susan Cohen, whose only child, Theodora, 20, was on the plane. "Everyone was surprised by this."

"This was strictly a political, commercial decision," she said in a telephone interview. "I'm not a fool. I know it's oil and money interests. At the end of World War II, if Adolf Hitler could have been brought back in the fold, would we have done it? And this isn't even the end of the war."

Although Libya signed the international treaty banning nuclear weapons in 1975 and a similar international ban on biological weapons in 1982, independent weapons experts said Colonel Qaddafi had been trying to obtain unconventional weapons for decades.

Writing in The Nonproliferation Review in 1997, Joshua Sinai, then a senior analyst at the Library of Congress, concluded that Libya had in fact developed a "rudimentary capability to produce such weapons," particularly chemical weapons, by the late 1980's.

Libya is one of the few nations that have consistently refused to sign the treaty banning chemical weapons. In a 1987 conflict with Chad, it became one of a handful of states to use such weapons in war, when it fired off Iranian-supplied mustard-gas bombs.

Washington has long accused Libya of producing blister and nerve agents at secret plants in Tarhuna, 50 miles southwest of Tripoli, and at the Pharma complex in Rabta, 75 miles southwest of Tripoli. Most of the chemical weapons seen by the visiting inspectors were at Rabta, one senior official said Friday.

Though Libya signed the treaty banning germ weapons in 1982, questions have remained about whether it was complying with the agreement.

Intelligence agencies have alleged, for instance, that Colonel Qaddafi attempted to recruit South African scientists to help him develop biological weapons. And American intelligence agents concluded earlier this year that Nizar Hindawi, a senior scientist who once led Iraq's germ weapons program, had tried to emigrate to Libya in the mid-1990's, officials said.

But many analysts continued to say that if Libya had a weapons program at all, the effort was very primitive, and years from producing biological weapons.

Matthew L. Wald contributed reporting for this article.