WASHINGTON — The intelligence community’s consensus-building body has commissioned a study on what President Bush has called the intolerable prospect of a nuclear Iran.

The study, contracted out last fall by the National Intelligence Council, the panel that brokers national intelligence estimates, will examine the implications of Iran developing nuclear weapons and whether a nuclear Iran would prompt Saudi Arabia, Egypt, and other Arab allies of America to pursue their own nuclear programs. “The NIC commissions studies on a wide range of national security issues,” a spokesman for the Directorate of National Intelligence, Carl Kropf, said. “Several of those studies are currently under way. However, I must decline to identify individuals or organizations conducting those studies, as well as their specific area of focus.”

The study on the implications of a nuclear Iran would be the NIC’s first examination of what might happen if Mr. Bush’s current Iran policy of financial sanctions, military posturing, and coercive diplomacy fails. The study also is likely to influence an upcoming National Intelligence Estimate on Iran’s nuclear program that is expected to re-examine the five- to 10-year time line for Iran’s acquisition of a nuclear weapon.

On April 13, 2006, the chairman of the NIC, Thomas Fingar, told Congress that Iran was still “several years away” from obtaining a nuclear weapon. Some dissenting analysts inside the intelligence community have said the view that Iran is 10 years away from attaining a nuclear weapon is based on the assumption that the country has no parallel, hidden military program.

Outside the classified world, tensions between America and Iran are at a boil. Iran’s supreme leader, Ayatollah Ali Khamenei, said yesterday that if America were to strike Iran, his country would attack American interests “all over the world.” And the Iranian intelligence minister, Gholamhossein Mohseni-Ejei, announced yesterday that he has identified 100 American and Israeli spies and that some have been arrested trying to leave the country.

On Sunday, the 10th day of Iranian celebrations commemorating the 1979 Islamic Revolution, Iran is expected to announce the completion of or progress on the installation of 3,000 centrifuges it has added to its declared nuclear enrichment facility at Natanz.

The American ambassador to the International Atomic Energy Agency, Gregory Schulte, said he expects an announcement along those lines. “Iranian authorities have told the world to expect a major nuclear announcement at this time,” he said. “Most analysts suspect it will involve the first steps toward large-scale uranium enrichment in the underground halls at Natanz. In fact, Mohamed ElBaradei has confirmed that Iranian technicians are moving ahead rapidly toward installing a 3,000-centrifuge capability.”

The expected announcement will fall 10 days before Mr. ElBaradei, the head of the IAEA, is scheduled to give an assessment of Iran’s cooperation with the nuclear inspections regime his agency now oversees. Last month, the Iranians expelled some inspectors from Iran, and last year, the chief inspector for Iran said publicly that Mr. ElBaradei had forced out him out of a job at the Iranians’ behest.

The NIC study also comes on the heels of what appears to be weakening European resolve on halting Iran’s nuclear program. Last month, President Chirac of France told reporters that an Iran with one or two nuclear bombs would not pose much of a danger. Though Mr. Chirac later retracted the remarks, a French presidential hopeful, Nicolas Sarkozy, has come out against any bombing of the Iranian facilities. “There can be no question of a military intervention,” he said Monday in an interview with French television.

The deputy director for research at the Washington Institute for Near East Policy, Patrick Clawson, said his biggest concern about a nuclear Iran “is for proliferation.” He said he expects that Saudi Arabia would counter an Iranian nuclear weapon by pursuing its own nuclear bomb, with Pakistan’s help. In 1987, the Saudis formally promised America that they would not build nuclear weapons after America did not object to the Chinese sale of intermediate missiles to Saudi Arabia.

Mr. Clawson also said a nuclear Iran would become more assertive regionally, arming groups such as Hezbollah and Hamas, possibly with advanced anti-tank and anti-plane systems. In 2002, the Israelis intercepted a ship loaded with military-grade explosives, the Karine A, that they said was headed to the Palestinian Authority from Iran.

A former CIA Iran and Iraq analyst, Kenneth Pollack, said yesterday that whether America could tolerate a nuclear Iran would depend on the current leadership of the regime. “I think at the end of the day, we could live with a nuclear Iran under the Khamenei leadership. From the death of Khomeini up to now, the Iranians have been nasty, murderous, and all those things, but they have not been reckless or irrational.”

But should President Ahmadinejad, who has called for Israel to be wiped off the map, amass real power, Mr. Pollack said he did not think Iran could be deterred.