MANAMA, Bahrain - Defense Secretary Robert M. Gates argued forcefully at a Persian Gulf security conference yesterday that U.S. intelligence indicates Iran could restart its secret nuclear weapons program "at any time" and remains a major threat to the region.

Tough and at times sarcastic, Gates described the Iranian government as an ongoing menace to the gulf region, not only for its nuclear aspirations but also for supplying weapons to insurgents in Iraq and Afghanistan, backing the armed Islamic movements Hezbollah and Hamas, and developing medium-range ballistic missiles.

"Everywhere you turn, it is the policy of Iran to foment instability and chaos, no matter the strategic value or cost in the blood of innocents," he said in a speech to defense leaders from 23 countries attending the Manama Dialogue, a security conference organized by the London-based International Institute for Strategic Studies.

Gates acknowledged that the recent release of a U.S. National Intelligence Estimate on Iran, which determined that the country halted its secret nuclear weapons program in 2003, was awkward and frustrating for the Bush administration.

"The estimate clearly has come at an awkward time. It has annoyed a number of our friends, it has confused our allies around the world," he said.

International pressure is the only impediment to Iran restarting its nuclear weapons program, Gates said. "Iran is keeping its options open and could restart its nuclear weapons program at any time - I would add, if it has not done so already."

Gates urged countries around the world to demand that Iran "come clean" about its past nuclear weapons development and insist that it suspend enrichment, pledge not to develop nuclear weapons in the future and agree to inspections. Until it takes those steps, he suggested, engaging Iran in talks would not be productive.

Iran maintains that its nuclear program is for peaceful energy purposes.

Iranian officials decided Friday not to attend the conference.

In questions following Gates' speech, attendees voiced both approval and suspicion. Some accused the United States of a double standard for failing to object to Israel's possession of nuclear weapons. Asked if he thought Israel's nuclear arsenal posed a threat to the region, Gates initially gave a four-word answer: "No, I do not."

To better counter Iran and other threats, Gates urged gulf nations to shift their focus from bilateral military ties with the United States toward multilateral cooperation. Specifically, he called for a collective effort to develop regional air and missile defense systems, as well as a shared monitoring of waters in the region for terrorism, piracy, drug trafficking and smuggling.

On Iraq, Gates said President Bush's troop increase over the last year has helped quell violence and demonstrated an enduring U.S. commitment to stabilizing the country. But he said the decline in U.S. troop levels starting this month represents "risks and opportunities for the whole region."

Arab nations should back the Iraqi government, Gates said, because if Iraq fails as a state, the repercussions would be felt first and most profoundly in the Middle East.