As tensions increase between the United States and Iran, U.S. intelligence and terrorism experts say they believe Iran would respond to U.S. military strikes on its nuclear sites by deploying its intelligence operatives and Hezbollah teams to carry out terrorist attacks worldwide.

Iran would mount attacks against U.S. targets inside Iraq, where Iranian intelligence agents are already plentiful, predicted these experts. There is also a growing consensus that Iran's agents would target civilians in the United States, Europe and elsewhere, they said.

U.S. officials would not discuss what evidence they have indicating Iran would undertake terrorist action, but the matter is consuming a lot of time throughout the U.S. intelligence apparatus, one senior official said. It's a huge issue, another said.

Citing prohibitions against discussing classified information, U.S. intelligence officials declined to say whether they have detected preparatory measures, such as increased surveillance, counter-surveillance or message traffic, on the part of Iran's foreign-based intelligence operatives.

Bigger threat than al-Qaeda?
But terrorism experts considered Iranian-backed or controlled groups -- namely the country's Ministry of Intelligence and Security operatives, its Revolutionary Guards and the Lebanon-based Hezbollah -- to be better organized, trained and equipped than the al-Qaeda network that carried out the Sept. 11, 2001, attacks.

The Iranian government views the Islamic Jihad, the name of Hezbollah's terrorist organization, as an extension of their state. . . . operational teams could be deployed without a long period of preparation, said Ambassador Henry A. Crumpton, the State Department's coordinator for counterterrorism.

The possibility of a military confrontation has been raised only obliquely in recent months by President Bush and Iran's government. Bush says he is pursuing a diplomatic solution to the crisis, but he has added that all options are on the table for stopping Iran's acquisition of nuclear weapons.

Speaking in Vienna last month, Javad Vaeedi, a senior Iranian nuclear negotiator, warned the United States that it may have the power to cause harm and pain, but it is also susceptible to harm and pain. So if the United States wants to pursue that path, let the ball roll, although he did not specify what type of harm he was talking about.

Rise in tension raises stakes
Government officials said their interest in Iran's intelligence services is not an indication that a military confrontation is imminent or likely, but rather a reflection of a decades-long adversarial relationship in which Iran's agents have worked secretly against U.S. interests, most recently in Iraq and Pakistan. As confrontation over Iran's nuclear program has escalated, so has the effort to assess the threat from Iran's covert operatives.

U.N. Security Council members continue to debate how best to pressure Iran to prove that its nuclear program is not meant for weapons. The United States, Britain and France want the Security Council to threaten Iran with economic sanctions if it does not end its uranium enrichment activities. Russia and China, however, have declined to endorse such action and insist on continued negotiations. Security Council diplomats are meeting this weekend to try to break the impasse. Iran says it seeks nuclear power but not nuclear weapons.

Former CIA terrorism analyst Paul R. Pillar said that any U.S. or Israeli airstrike on Iranian territory would be regarded as an act of war by Tehran, and that Iran would strike back with its terrorist groups. There's no doubt in my mind about that. . . . Whether it's overseas at the hands of Hezbollah, in Iraq or possibly Europe, within the regime there would be pressure to take violent action.

History of reprisals
Before Sept. 11, the armed wing of Hezbollah, often working on behalf of Iran, was responsible for more American deaths than in any other terrorist attacks. In 1983 Hezbollah truck-bombed the U.S. Marine barracks in Beirut, killing 241, and in 1996 truck-bombed Khobar Towers in Saudi Arabia, killing 19 U.S. service members.

Iran's intelligence service, operating out of its embassies around the world, assassinated dozens of monarchists and political dissidents in Europe, Pakistan, Turkey and the Middle East in the two decades after the 1979 Iranian revolution, which brought to power a religious Shiite government. Argentine officials also believe Iranian agents bombed a Jewish community center in Buenos Aires in 1994, killing 86 people. Iran has denied involvement in that attack.

Iran's intelligence services are well trained, fairly sophisticated and have been doing this for decades, said Crumpton, a former deputy of operations at the CIA's Counterterrorist Center. They are still very capable. I don't see their capabilities as having diminished.

Both sides have increased their activities against the other. The Bush administration is spending $75 million to step up pressure on the Iranian government, including funding non-governmental organizations and alternative media broadcasts. Iran's parliament then approved $13.6 million to counter what it calls plots and acts of meddling by the United States.

Given the uptick in interest in Iran on the part of the United States, it would be a very logical assumption that we have both ratcheted up [intelligence] collection, absolutely, said Fred Barton, a former counterterrorism official who is now vice president of counterterrorism for Stratfor, a security consulting and forecasting firm. It would be a more fevered pitch on the Iranian side because they have fewer options.

Agencies mum on true threat
The office of the director of national intelligence, which recently began to manage the U.S. intelligence agencies, declined to allow its analysts to discuss their assessment of Iran's intelligence services and Hezbollah and their capabilities to retaliate against U.S. interests.

We are unable to address your questions in an unclassified manner, a spokesman for the office, Carl Kropf, wrote in response to a Washington Post query.

The current state of Iran's intelligence apparatus is the subject of debate among experts. Some experts who spent their careers tracking the intelligence ministry's operatives describe them as deployed worldwide and easier to monitor than Hezbollah cells because they operate out of embassies and behave more like a traditional spy service such as the Soviet KGB.

Other experts believe the Iranian service has become bogged down in intense, regional concerns: attacks on Shiites in Pakistan, the Iraq war and efforts to combat drug trafficking in Iran.

As a result, said Bahman Baktiari, an Iran expert at the University of Maine, the intelligence service has downsized its operations in Europe and the United States. But, said Baktiari, I think the U.S. government doesn't have a handle on this.

Facilities make difficult targets
Because Iran's nuclear facilities are scattered around the country, some military specialists doubt a strike could effectively end the program and would require hundreds of strikes beforehand to disable Iran's vast air defenses. They say airstrikes would most likely inflame the Muslim world, alienate reformers within Iran and could serve to unite Hezbollah and al-Qaeda, which have only limited contact currently.

A report by the independent commission investigating the Sept. 11 attacks cited al-Qaeda's long-standing cooperation with the Iranian-back Hezbollah on certain operations and said Osama bin Laden may have had a previously undisclosed role in the Khobar attack. Several al-Qaeda figures are reportedly under house arrest in Iran.

Others in the law enforcement and intelligence circles have been more dubious about cooperation between al-Qaeda and Hezbollah, largely because of the rivalries between Shiite and Sunni Muslims. Al-Qaeda adherents are Sunni Muslims; Hezbollah's are Shiites.

Iran certainly wants to remind governments that they can create a lot of difficulty if strikes were to occur, said a senior European counterterrorism official interviewed recently. That they might react with all means, Hezbollah inside Lebanon and outside Lebanon, this is certain. Al-Qaeda could become a tactical alliance.

Researcher Julie Tate contributed to this report.

The same officials believe that a failure of the controversial constitution - which Sunnis say favours the Shia majority - would require at least another year of political negotiations, threatening any plans to disengage.