WASHINGTON - Prompted by evidence that Iran is harboring top al-Qaida operatives linked to last week's suicide bombings in Saudi Arabia and fears that Tehran may be closer to building a nuclear weapon than previously believed, the Bush administration has begun debating whether to take action to destabilize the Islamic republic, U.S. officials said Thursday.

Officials in Defense Secretary Donald H. Rumsfeld's office are using both issues to press their view that the United States should adopt both overt and covert measures to undermine the Islamic regime in Tehran, said the officials, who are involved in the debate. Other officials argue that such a campaign would backfire by discrediting the moderate Iranians who are demanding political reforms.

Although one senior official engaged in the debate said "the military option is never off the table," others said no one was suggesting an invasion of Iran, although some officials think the United States should launch a limited air strike on Iran's nuclear weapons facilities if Iran appears on the verge of producing a nuclear weapon. By some estimates, Iran could have a nuclear weapon within two years.

Some Pentagon officials suggested using the remnants of an Iranian opposition group once backed by Saddam Hussein, the Mujahedeen Khalq (MEK), to instigate armed opposition to the Iranian government. U.S. military forces in Iraq have disarmed the roughly 6,000-strong MEK, which is on the State Department's list of foreign terrorist groups. But the group's weapons are in storage and it hasn't disbanded.

However, national security adviser Condoleezza Rice and other top officials rejected the idea, saying that while some might consider the MEK freedom fighters, "a terrorist is a terrorist is a terrorist," according to officials involved in the debate.

Bush has designated Iran a member of an "axis of evil," along with Iraq and North Korea. But until now, he's pursued a middle course with Iran, OK'ing talks on issues of common concern such as Afghanistan, while not attempting to re-establish diplomatic ties.

A formal statement of U.S. policy toward Iran, called a National Security Presidential Directive, has been on hold about a year because of internal administration debates and the war in Iraq, American officials said. The document is being resurrected, they said.

Bush's senior foreign-policy advisers were to have met at the White House on Thursday to discuss Iran policy, said a knowledgeable administration official, but the meeting was postponed until next week to give Iran several more days to meet U.S. demands that it turn over the suspected al-Qaida terrorists. If it doesn't, Washington is likely to react with harsher measures, the official said.

The United States has suspended a series of meetings between U.S. and Iranian diplomats in Geneva at which the two countries - which have no formal diplomatic relations - have been discussing terrorism, Afghanistan and Iraq.

The suspension followed intelligence data, including intercepted telephone calls, indicating that an al-Qaida cell based in Iran helped organize the bombings in Riyadh, Saudi Arabia, which were apparently part of a larger al-Qaida plot that was partially foiled by Saudi authorities. The bombings killed 34 people, eight of them Americans.

The cell of 10 or so al-Qaida members is run by top al-Qaida operative Saif al Adel, who is third on the U.S. government's list of most-wanted al-Qaida leaders, following Osama bin Laden and his deputy Ayman al Zawahri.

"There's no question but that there have been and are today senior al-Qaida leaders in Iran, and they are busy," Rumsfeld said this week.

Iranian officials have denied harboring al-Qaida fugitives, and U.S. officials acknowledge that Iran has turned over some al-Qaida suspects to Saudi Arabia and Pakistan and blocked others from entering its territory.

The senior U.S. intelligence official said it wasn't clear whether al Adel's group, which is believed to be in a remote area of southeastern Iran near the border with Pakistan, was operating with the acquiescence of at least part of the Iranian government.

Also driving the Bush administration's concern - as well as that of Israel - are revelations that Iran's nuclear weapons program may be far more advanced than previously believed.

Last summer, the MEK alleged that Iran was building a uranium enrichment plant near the city of Natanz, unknown to U.S. intelligence agencies.

The United States is pushing the International Atomic Energy Agency to declare Iran in violation of the 1968 nuclear Nonproliferation Treaty. IAEA chief Mohamed ElBaradei is due to issue a report on Iran on June 10.

The Bush administration will announce Friday that it's imposing sanctions on a Chinese firm, North China Industries, for transferring technology that aided Iran's ballistic missile program. The sanctions also will apply to an Iranian firm, the Shahid Hemmat Industrial Group.

Advocates of regime change want to bolster popular opposition in Iran to the religious leadership, which has used its supreme power to block much of President Mohammed Khatami's reform agenda and is despised by many Iranians.

Sen. Sam Brownback, R-Kan., introduced legislation Monday that would expand pro-democracy broadcasting into Iran and commit the United States to backing an internationally monitored referendum allowing Iranians to change their government peacefully.

Flynt Leverett, a former White House and CIA official, said advocates of that approach overestimated the weakness of the Iranian government.

"I don't think the Iranian regime as a whole is a house of cards just ready to be pushed over," said Leverett, who's now at the Washington-based Brookings Institution's Saban Center for Middle East Policy.

It's particularly unlikely that a new government would be in place in Tehran in time to address U.S. concerns over Iran's nuclear weapons program and similar issues, Leverett said.

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