WASHINGTON -- The White House acknowledged Wednesday that its hunt for Iraqi weapons of mass destruction -- a two-year search costing millions of dollars -- has closed down without finding the stockpiles that President Bush cited as a justification for overthrowing Saddam Hussein. Bush's spokesman said the president had no regrets about invading Iraq.

"Based on what we know today, the president would have taken the same action because this is about protecting the American people," said Press Secretary Scott McClellan.

The Iraq Survey Group -- made up of as many as 1,500 military and intelligence specialists and support staff -- is ending its search of military installations, factories and laboratories where it was thought that equipment and products might be converted to making weapons.

McClellan said the active search had virtually ended. "There may be a couple, a few people that are focused on that," he said, adding that they would handle any future reports that might come in.

At a meeting last month, McClellan said Bush thanked the chief U.S. weapons inspector, Charles Duelfer, for his work. A special adviser to the CIA director, Duelfer will deliver a final edition of a report on Iraq's weapons next month. McClellan said it is not expected to fundamentally differ from the findings of a report last fall.

Duelfer said then that Iraq had no weapons of mass destruction and had not made any since 1991. However, he said the government harbored intentions of recreating its weapons programs and had gone to great lengths to manipulate the U.N. oil-for-food program.

In an interview Wednesday with Barbara Walters of ABC News, Bush defended his decision to invade Iraq.

"I felt like we'd find weapons of mass destruction -- like many here in the United States, many around the world," Bush said in the interview, to be broadcast Friday night. "We need to find out what went wrong in the intelligence gathering. ... Saddam was dangerous and the world is safer without him in power."

In a statement, House Democratic leader Nancy Pelosi of California said Bush "needs to explain to the American people why he was so wrong, for so long, about the reasons for war."

The end of the weapons hunt comes as the Bush administration struggles with a dangerous security situation in Iraq leading up to Jan. 30 elections.

Meanwhile, other countries -- notably Iran and North Korea -- are suspected of developing covert nuclear weapons programs.

When asked whether the failure to find weapons of mass destruction in Iraq would damage U.S. credibility in handling future threats, McClellan said the president would continue to work with the international community, particularly on diplomatic solutions. He said pre-emptive military action was "the last option" to pursue.

"We are acting to make sure we have the best possible intelligence," McClellan said, adding that a number of changes have been made since the Sept. 11, 2001, attacks.

Almost one year ago, Bush formed a presidential commission to investigate U.S. intelligence capabilities on weapons of mass destruction, focusing not only on Iraq but on how well the intelligence community understands the threat from other countries and terror networks. Its report is due March 31.

The closing down of the weapons search was first reported in the Washington Post on Wednesday.

David Kay, who headed the Iraq Survey Group until stepping down last January, said he was not surprised the group was concluding its efforts without finding any major weapons stockpiles.

"It is like dropping a shoe a little late. Quite frankly, I don't think anyone who follows it very closely has suspected anything else over the last year. It was a matter of when the obvious would be done," Kay said.

He said that intelligence analysts working in Iraq had found themselves in a dangerous security situation and that many had reached conclusions about the lack of weapons as much as 18 months ago. "How do you keep them motivated?" he asked.

At the State Department, spokesman Richard Boucher said the U.S. government was paying stipends to about 120 Iraqi scientists who once had been working in weapons programs. They now are working on scientific research outside weapons development.

Greg Thielmann, the former manager of the State Department office that tracked chemical, biological and nuclear weapons issues, said the United States should devote energy to employment of these scientists, who now appear to have been involved in non-weapons work under Saddam in recent years.

"Who knows what they are going to do?" asked Thielmann, who left his position in September 2002. "One can question whether we improved the security situation through the invasion."