British Prime Minister Tony Blair and his senior ministers on Monday weighed their military options for joining the U.S. war on terrorism after being briefed on U.S. battle plans, and a spokesman said there was "a clear likelihood" of military action.

Lt. Gen. Anthony Pigott, the deputy chief of defense staff, informed Blair and other officials about talks with Pentagon officials in Washington in recent days to establish the precise role the U.S. wants Britain to play in the conflict. Some unconfirmed reports said the U.S. wants to call on British special forces and Royal Air Force reconnaissance aircraft.

Blair also briefed members of four parliamentary committees. Parliament is not in session but will have to be recalled if military action begins.

The British aircraft carrier HMS Illustrious passed through the Suez Canal on Monday en route to the Arab Persian Gulf state of Oman, where 17,500 British soldiers have been scheduled for months to take part in a joint exercise with Omani troops in two weeks. Among them are units of the Special Air Services, the equivalent of U.S. Special Forces, trained to operate clandestinely behind enemy lines and to conduct small-scale operations.

Mountain training

A unit of the SAS has trained in the Pakistani mountains for the last five years, which would prepare the troops for duty in the steep terrain of Afghanistan. But defense officials here declined to say whether elements of the Oman exercise would be used in Afghanistan.

The Illustrious has an air wing that could be useful in Afghanistan. It consists of 15 Sea Harriers and Harrier GR7s. Seven Tornado GR4 fighter-bombers also have been sent to Oman since the crisis began. HMS Trafalgar, a nuclear-powered submarine with Tomahawk land-attack cruise missiles, also could take part in operations against Afghanistan.

There has been speculation that two squadrons of the SAS, about 100 men, could operate out of Uzbekistan along with American forces. Uzbekistan, a former Soviet republic with a large Muslim population, borders Afghanistan on the north.

Minister visits Iran

Foreign Secretary Jack Straw flew to Jordan on Monday as part of Britain's effort to line up the widest possible international support for a war on terrorism. He then flew to Iran, the first visit there by a British foreign secretary since the 1979 Islamic revolution that overthrew Shah Mohammed Reza Pahlavi.

Iran has condemned the Sept. 11 attack on the U.S. and has been at odds with the Taliban regime in Afghanistan. Straw said he would not seek Iranian military participation but would request diplomatic support and would discuss the Israel-Palestine conflict. The most important aspect of contacts with Iran, he said, is that the Iranian stand against the Taliban demonstrates "that this is not a fight with Islam or Islamic people."

Police in Tehran broke up a demonstration Monday outside the British Embassy protesting Straw's visit and arrested about 50 people. "Death to America! Death to Britain!" the group chanted.

Straw said of the coming conflict: "There will be risks, and there will be casualties, and that is a very heavy responsibility on all those having to make decisions. But it is obviously very much worse for those taking the risks and for their families."

Northern Ireland Secretary John Reid delivered a similar warning about British casualties on Sunday.

On the home front, the government is gearing up for tighter security measures, including the possible introduction of compulsory identification cards for all residents. While many West European nations have used ID cards for years, they were abolished in Britain by former Prime Minister Winston Churchill in 1953, and there is strong opposition from civil liberty groups to their reintroduction.

The government also is considering new police powers to interrogate suspects and the abolition of some rights of judicial appeal for immigrants refused entry at British ports. This could include allowing police to arrest for questioning people suspected of having knowledge of terrorist activities.

Majority call for action

While polls show 65 percent of Britons support military action against terrorists, an antiwar movement also is being organized. A weekend rally outside government offices drew about 4,000 people.

The Liberal Democrat Party opened its annual conference Monday with leader Charles Kennedy chiding Blair and President Bush for their talk of war, and Bush for his use of the word "crusade."