President Bush said Monday that force is not necessarily required to stop Iran from having a nuclear weapon, and he dismissed reports of plans for a military attack against Tehran as "wild speculation."

Bush said his goal is to keep the Iranians from having the capability or the knowledge to have a nuclear weapon.

"I know we're here in Washington (where) prevention means force," Bush said during an appearance at the Paul H. Nitze School of Advanced International Studies at Johns Hopkins University. "It doesn't mean force necessarily. In this case it means diplomacy."

Taking questions from the audience, Bush also made these points:

—He declassified part of a prewar intelligence report on Iraq in 2003 to show Americans the basis for his statements about the threat posed by Saddam Hussein. "I wanted people to see the truth," he told a questioner who said there was evidence of a concerted effort by the White House to punish war-critic Joseph Wilson. Bush said he could not comment on the CIA leak case because it is a matter under investigation.

—He intends to remain on the sidelines as Republicans choose their nominee for president in 2008. "I will be an interested observer," said Bush. He said he would focus his energy on issues such as decreasing the nation's reliance on foreign oil and finding answers to the solvency problems of Medicare and Social Security. "But I'm just going to let the politics run its course."

Bush and other administration officials have said repeatedly that the military option is on the table, and White House officials acknowledge "normal" military planning is under way. Several reports published over the weekend said the administration was studying options for military strikes, and an account in The New Yorker magazine raised the possibility of using nuclear bombs against Iran's underground nuclear sites.

Bush did not directly respond to that report but said, "What you're reading is just wild speculation."

But Bush said he was correct to include Iran in the "axis of evil" with Iraq and North Korea and that he's glad to see other countries taking the threat from Iran seriously, too.

"I got out a little early on the issue by saying 'axis of evil,"' Bush said. "But I meant it. I saw it as a problem. And now many others have come to the conclusion that the Iranians should not have a nuclear weapon."

The White House sought Monday to minimize new speculation about a possible military strike against Iran while acknowledging that the Pentagon is developing contingency plans to deal with Tehran's nuclear ambitions. The Pentagon has refused to describe its planning further.

White House press secretary Scott McClellan refused to confirm or deny The New Yorker report. "Those who are seeking to draw broad conclusions based on normal military contingency planning are misinformed or not knowledgeable about the administration's thinking," he said.

British Foreign Secretary Jack Straw, in an interview Sunday with the British Broadcasting Corp., called the idea of a nuclear strike "completely nuts."

Straw said Britain would not launch a pre-emptive strike on Iran and he was as "certain as he could be" that neither would the U.S. He said he has a high suspicion that Iran is developing a civil nuclear capability that, in turn, could be used for nuclear weapons, but he said there is "no smoking gun" to prove it and rationalize abandoning the plodding diplomatic process.

"The reason why we're opposed to military action is because it's an infinitely worse option and there's no justification for it," Straw said.

Defense experts say a military strike on Iran would be risky and complicated. U.S. forces already are preoccupied with Iraq and Afghanistan, and an attack against Iran could inflame U.S. problems in the Muslim world.

The U.N. Security Council has demanded Iran suspend its uranium enrichment program. But Iran has so far refused to halt its nuclear activity, saying the small-scale enrichment project was strictly for research and not for development of nuclear weapons.

Bush has said Iran may pose the greatest challenge to the United States of any other country in the world. And while he has stressed that diplomacy is always preferable, he has defended his administration's strike-first policy against terrorists and other enemies.

"The threat from Iran is, of course, their stated objective to destroy our strong ally Israel," the president said last month in Cleveland. "That's a threat, a serious threat. It's a threat to world peace; it's a threat, in essence, to a strong alliance. I made it clear, I'll make it clear again, that we will use military might to protect our ally."