LONDON, JAN. 18 -- Britain has quickly reasserted its role as the United States's closest and most reliable ally through its intimate diplomatic, military and intelligence collaboration with Washington during the Persian Gulf War, according to officials and analysts here.

Analysts say cooperation has returned to Cold War and even World War II levels, belying claims that the collapse of the Soviet bloc would lead to a new world order in which the old Atlantic alliance between Washington and London would have to give way to greater U.S. cooperation with European powers such as France and Germany.

French forces are contributing to the multinational effort in the gulf, but under special restrictions, while Germany appears deeply divided and hesitant. Only Britain has given unswerving support, committing an estimated 35,000 troops and other personnel, 75 warplanes and 15 ships to overall American command without complaint or reservation.

In addition, the Associated Press reported today that Britain will send to the gulf a 500-member battalion from the elite Coldstream Guards to help run allied prisoner of war camps, and a 206-member reserve air force squadron to help with logistical support.

"Britain by and large has wielded an influence out of all proportion to the numbers there because it is the one dependable ally that doesn't try to do fancy diplomacy around the edges," said historian Peter Henessey, an authority on British-American relations.

Before the war broke out, Britain served in effect as America's agent inside the European Community, heading off various attempts at separate diplomatic initiatives proposed by the French, Germans and Italians. Now that the war has begun, British forces are carrying out specialized missions that include targeting and destroying Iraqi airfields and radar installations. Four British airmen are listed as missing since the start of the fighting.

The level of cooperation among military commanders on the ground in Saudi Arabia appears matched by close collaboration between London and Washington. President Bush and Prime Minister John Major have had almost daily phone contact beginning Tuesday, while Brent Scowcroft and Charles Powell, Bush and Major's respective national security advisers, are said to speak to each other several times a day.

"There's a remarkable degree of coordination -- even the statements coming out of officials in the two capitals are extraordinarily similar," said Hans Binnendijk, security analyst at the International Institute for Strategic Studies here.

Binnendijk said there has been an extraordinary reversal of roles in recent weeks between Germany and Britain. The Germans, who received unwavering American support as they unified, have failed to reciprocate on the gulf, while the British have delivered, he said.

"I think the American-German relationship is in for a very rough road, while American-British relations are as strong as ever," he said.

Although there have been anti-war marches and an increasingly vocal minority arguing for peace, the British establishment has been far more firmly united behind government policy than its American counterpart. So has the British press, with all 21 national newspapers supporting the war in recent days.

The leadership of the opposition Labor Party, which fears being portrayed as too far to the left, has also backed the government, even though Labor leaders say they would have preferred to give economic sanctions more time to work. The House of Commons voted earlier this week, 453 to 57, to back government policy -- a dramatic contrast to the narrower margins of victory in the U.S. Congress.

Just as the Vietnam War remains the defining moment for American politicians and military leaders, British officials look to the 1982 Falklands war, a successful and far less traumatic exercise in modern warfare. That is one of the reasons why Britain appears less fearful about going to war.

Another is the fact that Britons on both the right and left have a greater sense of respect for the United Nations than do Americans. Labor Party leader Neil Kinnock has repeatedly cited U.N. resolutions as justification for his support for the war. The British also are more prepared to accept a role in protecting countries like Kuwait and Saudi Arabia, both of which once fell under British colonial suzerainty.

Critics say Britain also has less of a tradition of open debate about security issues. "Prewar doubts have been aired more fully {in the United States}, without critics being tarred as traitors," wrote columnist Peter Kellner in the Independent.

While the Falklands was a victory, officials here say that conflict suggests public support for the gulf war may begin to collapse if the fighting continues for more than a month. They are particularly concerned about American morale and public opinion, which they fear is highly volatile.

"We are sure President Bush is determined to see this through and we were glad to see Congress supporting him," said one senior official. "But the sooner it's over, the better."

The other factor holding together British opinion has been Major, the new prime minister, who has adopted a far more restrained and conciliatory tone with his political opponents here than did his more combative predecessor, Margaret Thatcher.

Aides say Major, who has little foreign policy experience, came into office two months ago believing Iraqi President Saddam Hussein eventually would back down over Kuwait. Only in recent weeks did Major gradually come to the conclusion that conflict was inevitable.

Nonetheless, Major has taken charge in a quiet, low-key manner, welcoming Kinnock's support and repeatedly refusing opportunities to divide the opposition or criticize press coverage -- two of Thatcher's favorite political pastimes.

Major meets daily with a "war cabinet" composed of Foreign Secretary Douglas Hurd, Defense Secretary Tom King and Energy Secretary John Wakeham, along with Chancellor of the Exchequer Norman Lamont and Attorney General Sir Patrick Mayhew. Aides say he has come to realize that his fate is largely in U.S. hands -- that this unexpected and unwelcome crisis could make or break his young premiership even though the crucial decisions will be made by Washington.

"If the war goes well . . . he may be prime minister for a decade," opined the Economist magazine. "If he stumbles, he is history."