TEHRAN, Iran -- Iran has begun publicly preparing for a possible U.S. military attack, announcing efforts to mobilize recruits in citizens' militias and making plans to engage in the type of "asymetrical" guerrilla warfare which has bogged down American troops in neighboring Iraq.

"Iran would respond within 15 minutes to any attack by the United States or any other country," said an Iranian official close to the conservatives who run the country's security and military apparatus.

Tensions between Tehran and Washington have been escalating over Iran's pursuit of nuclear technology. Tehran insists it needs nuclear power to meet its burgeoning domestic energy needs and to bolster its scientific community. Washington accuses Iran of using nuclear energy as a fig leaf for a weapons program.

France, Great Britain and Germany, also suspicious of Iran's nuclear ambitions, have insisted on strict inspections while urging Iran to give up potential weapon-making components of its nuclear program.

On his trip to Europe last week, President Bush said he supported European diplomatic efforts and labeled as "ridiculous" suggestions that the United States was getting ready to attack Iran. Nonetheless, he refused to rule out the use of military force to stop Iran from developing a nuclear weapon. The Pentagon recently revealed that it had upgraded its Iranian war plans as a matter of routine preparedness.

Meanwhile, Iranian authorities say they also are getting ready in case of war.

Newspapers have announced efforts to increase beyond 7 million the number of "Basiji" militia, which were deployed in human wave attacks against Saddam Hussein's army during the Iran-Iraq war of the 1980s. Iranian military authorities have paraded long-range North Korean-designed Shahab missiles before television cameras. Iranian generals have conducted massive war games near the Iraqi border.

One Western military expert based in Tehran said Iran was sharpening its ability to wage a guerrilla war.

"Over the last year they've developed their tactics of asymmetrical war, which would aim not at resisting a penetration of foreign forces, but to then use them on the ground to all kinds of harmful effect," he said, on condition of anonymity.

It remains unclear how much of the recent military activity amounts to mobilization and how much may be a propaganda ploy. Iranian officials and analysts have said they want to highlight the potential costs of an attack on Iran to frighten a war-weary American public and make U.S. officials think more than twice about launching one.

"Right now it's a psychological war," said Nasser Hadian, a University of Tehran political science professor who recently returned from a three-year stint as a scholar at Columbia University in New York.

"If America decides to attack, the only ones who could stop it are Iranians," he said. "Pressure from other countries and inside America is important, but it won't prevent an attack. The only thing that will prevent an attack is that if America knows it will pay a heavy price."

Iran is also attempting to give the impression that it is bolstering its conventional forces. Last December, Iran announced its largest war games "ever," deploying 120,000 troops as well as tanks, helicopters and armored vehicles along its western border. More recently, the Iranian press reported that the air force had received orders to engage any plane that violates Iranian airspace, just after reports emerged that American spy drones were monitoring Iran's nuclear sites.

"It is obvious that with Iran surrounded by the United States forces [in Iraq and Afghanistan] and America pressing the nuclear issue, Iran wants to make a show of force," said a Western diplomat in Tehran, speaking on condition of anonymity.

Iran's army includes 350,000 active-duty soldiers and 220,000 conscripts. Its elite Revolutionary Guard numbers another 120,000. Its Navy and Air Force total 70,000.

The armed forces can call on 2,000 tanks, 300 combat aircraft, three submarines, hundreds of helicopters and at least a dozen Russian-made Scud missile launchers. Iran also has an undetermined number of Shahab missiles based on North Korean designs with ranges of more than 1,500 miles.

Both outside military experts and Iranians concede that the country's antiquated conventional hardware, worn down by years of U.S. and European economic sanctions, would pose no challenge to the high-tech weaponry of the United States.

"Most of Iran's military equipment is aging or second rate, and much of it is worn," wrote military expert Anthony Cordesman in a December assessment.

At a recent military demonstration in the northwestern city of Qazvin, the western military expert said he spotted 30-year-old American-made M113 tanks. "Those tanks were able to go a few a meters in front of us," he said. "But in a combat situation? I don't know."

Still, Iran could create troubles for Washington and the world if war were to break out.

Iran's intelligence agencies have extensive overseas experience, experts say, and its highly classified Quds forces, which answer directly to Iranian leader Grand Ayatollah Ali Khamenei, are believed to have operations in Lebanon, Palestine, Jordan, Afghanistan, Pakistan, India, Turkey, the Persian Gulf, Central Asia and North Africa, as well as Europe and North America, according to a December 2004 report prepared by the Center for Strategic and International Studies.

Within minutes of attack, Iran's air and sea forces could threaten oil shipments in the Persian Gulf and Gulf of Oman. Iran controls the northern coast of the Strait of Hormuz, the narrow waterway through which oil tankers must navigate to get out of the Persian Gulf, and it could sink ships, mine sea routes or bomb oil platforms to block it.

Iran also could activate Hezbollah militia in Lebanon to launch attacks on Israel. Operatives could attack U.S. interests in Azerbaijan, Central Asia or Turkey.

"Iran can escalate the war," said Hadian. "It's not going to be all that hard to target U.S. forces in these countries."

But most analysts agree that the biggest trump card Iranians could play would be to unleash havoc in neighboring Iraq, where Iraqis who spent years in Iran as exiles are about to assume control of the government.

Although the U.S. alleges Tehran already has been meddling in Iraq, many brush off the current low-level infiltration as minor compared to the damage Iran could cause by arming Iraqi militias and providing them sanctuary, by backing extreme Islamist groups instead of the moderates it now supports, or by dispatching operatives across the long porous border to exacerbate the Iraqi insurgency.

Any Iranian retaliation "would surely start with attempts to mobilize Shiite partisans in Iraq to try to turn the Iraqi south into an extension of the insurgency in the Sunni triangle," said Gary Sick, a professor of Middle East studies at Columbia University and a former security adviser to President Jimmy Carter, in recent congressional testimony.

Despite rising tension, Iran remains quiet and there is little public evidence of a military call-up. It is unclear whether most young Iranian men -- more materialistic and middle class than the generation that fought for eight years against Iraq in the 1980s -- would fight with much enthusiasm against the United States.

Hamid-Reza, a 23-year-old clothing store manager who lost numerous relatives in the Iran-Iraq war, said he would definitely be willing to fight but feared that Iran would prove no match for the United States.

"What will I do?" he asked. "Get inside an inner tube and go fight against the American battleships in the Persian Gulf?"