President Bush said today that Iran must abandon any ambitions to build nuclear weapons and vowed to maintain international diplomatic pressure on the Iranian government.

Addressing an "Ask President Bush" event on the campaign trail in Northern Virginia, Bush expressed concern about Iran's nuclear program, but stopped short of any threat to use force to head off the development of atomic arms.

His comments came amid growing worry in Europe over Iranian insistence on having access to advanced nuclear technology, including "dual-use" equipment and know-how that can be applied to building nuclear weapons as well as power-generating programs.

Responding to a question from the audience about the Iranian "nuclear threat" during an appearance at Northern Virginia Community College in Annandale, Bush said, "First of all, you've got to understand that every situation requires a different response when it comes to foreign policy. And so we tailor our responses based upon the reality of the moment. And, first, just to make it clear to the world that Iran must abandon her nuclear ambitions. That's part of the role of the United States, and to work with others to send that same message."

Bush said the United States is "working closely" with the International Atomic Energy Agency on the Iranian issue.

"We're making sure that we ask the hard questions to the IAEA, so they ask the hard questions to the Iranians," he said.

But he said that since the United States itself has no diplomatic relations with Iran and already has "totally sanctioned them," his government has limited options in dealing with the Islamic republic. "In other words . . . we're out of sanctions" that can be applied by the United States, Bush said, "and so we've relied upon others to send the message for us."

Accordingly, Bush said, "the foreign ministers of Germany, France and Great Britain have gone in as a group to send a message on behalf of the free world that Iran must comply with the demands of the free world. And that's where we sit right now."

Bush added, "We've got to continue to keep pressure on the [Iranian] government, and help others keep pressure on the government, so there's kind of a universal condemnation of illegal weapons activities."

On Sunday, Condoleezza Rice, Bush's national security adviser, said in an interview on CNN that the United States has led the way in convincing the international community that "Iran was trying, under the cover of a civilian nuclear program, to actually bring about a nuclear weapons program."

But Rice would not say whether the United States would take unilateral action to end the program.

"I think we've finally now got the world community to a place, and the [IAEA] to a place, that it is worried and suspicious of the Iranian activities," Rice said. "Iran is facing for the first time real resistance to trying to take these steps."

In a meeting last week in Paris, however, Iran demanded European backing for its quest to obtain "dual-use" nuclear technology and called for the removal of sanctions designed to prevent such access, the Associated Press reported.

The stand dismayed the Europeans and strengthened a U.S. push for United Nations sanctions against Iran, the agency reported.

In a list of demands presented at a meeting with senior French, British and German negotiators, Iran called on the three countries to support its access to "advanced [nuclear] technology, including those with dual use," according to the AP.

Iran also demanded that the three "remove impediments" to obtaining such technology, resist potential U.N. Security Council sanctions, meet Iran's conventional weapons requirements and "provide security assurances" against a nuclear attack on Iran.

The IAEA is scheduled to meet next month to review Iran's nuclear program.

Iran insists that it wants dual-use technology, such as uranium enrichment, only to help generate nuclear power to meet its electricity needs.

A vast nuclear power program was begun by the shah of Iran in the 1970s, but it stalled after he was ousted by an Islamic revolution in 1979. In recent years, the ayatollahs running the country have sought to revive the program, resuming work on a nuclear power plant in southern Iran that a German company had nearly completed at the time of the revolution.

Although there were concerns during the shah's reign that he had ambitions to build nuclear weapons, the United States did not oppose his nuclear power program, and U.S. companies were among those that sought to obtain multibillion-dollar contracts to build the plants.