If the United States and the Soviet Union were posed in the Persian Gulf on the brink of military confrontation, would troops and ships of America's allies be there alongside U.S. forces?

Though the question is simple, the answer, is complicated, because U.S. planners don't want of the North Atlantic Treaty Organization in Western Europe, where most NATO forces face the great bulk of Soviet-led Warsaw Pact armies across the West German border.

Many planners believe that a U.S. Soviet confrontation in the Persian Gulf could quickly spread to Europe, where Western and U.S. interests ultimately are greater.

From interviews with White House State Department and Pentagon officials, it seems probable that the United States does not expect any large-scale military support on the scene in the Persian Gulf from Western Europe, and none from Japan, whose forces are too small and far away.

Rather, the United States wants its allies to improve their own defense and mobilization readiness in Europe, a move that could free additional U.S. forces -- basically those held in reserve in the United States -- for action in the Gulf.

Thus far, contacts with America's allies have been aimed at securing access routes, overflight permission and bases in the Indian Ocean.

But if the United States ever is going to fight, it will need real help, mostly in the form of navel forces, say specialists. Top-level officials suggest a policy is emerging that is meant to bring more pressure on this country's allies in forthcoming meetings.

Despite months of turmoil in the Persian Gulf, the issue of whether only U.S. troops should fight for the region's oil -- which is more important to Japan and Western Europe than to the United States -- is a question that largely had not been faced either here or abroad.

Yet this is a potentially explosive issue that could make a large dent in American public opinion, which now supports President Carter's pledge to defend the Persian Gulf.

Planners say privately that only Australia has indicated a willingness to put forces on the line in the Persian Gulf in the form of a small naval task force of frigates, gunboats and one oiler.

Britain's Royal Navy, in a move little noted at the time, last month diverted three frigates and sent them into the Mediterranean as a political signal to back up Britain's condemnation of the Soviet invasion of Afghanistan.

The British move demonstrates one potential form of help for the United States outside the Persian Gulf flash point. If allied navies from Britain, France, Italy and West Germany increase their presence in the Mediterranean, more elements of the U.S. Sixth Fleet there could redeploy to the Gulf.

Britain and France are the nations that could be most helpful militarily. Both have sizable navies able to help protect the sea lanes. Though the British withdrew militarily from east of Suez in 1971, they still have considerable operating expertise in the region.

The French have the largest permanent naval presence in the Indian Ocean, with four heavily armed frigates and a command ship based at Djibouti, along with some 4,000 troops, plus about eight other support vessels, destroyers and patrol ships in the region, most operating out of La Reunion island.

Djibouti and the British Indian Ocean base at Diego Garcia, already available to the United States, could be crucial for any swift buildup of U.S. forces to the region.

But would France commit forces to battle? Though they are potentially the most important, and cooperation is good between U.S. and French military leaders, political relations between the Carter administration and the government of Giscard d'Estaing are worse than with any other ally.

While France has condemned Soviet actions and reaffirmed its support of NATO, it remains outside the military side of the alliance and 'Estaing has given no indication, officials say, that he would commit French forces in the Persian Gulf.

But there also is no indication these officials add, that the United States has yet raised this question with the French or its other allies.

U.S. efforts to get the Soviets out of Afghanistan thus far have been aimed at raising the cost to the Kremlin through grain and trade cutoffs and the Olympic boycott.

U.S. officials acknowledge, however, that there still is no agreed military strategy for bringing its allies into defense of the Persian Gulf region if necessary.

Under any circumstance, the United States would have have to bear the brunt of a Soviet confrontation. But the lack of discussion and agreement with its allies on the wisdom and form of possible military responses, or even if the situation could be handled militarily, is creating confusion and dissension in the NATO alliance that could lead to important changes in attitudes and commitments.

For example, although there is no plan to shift any of the 200,000 U.S. Army troops in West Germany, U.S. planners say there is discussion about whether to continue stockpiling heavy arms and equipment in Europe for U.S. reinforcements that might now be targeted elsewhere.

The removal of a U.S. aircraft carrier from the Western Pacific near Japan to support the new Indian Ocean task force is a move that could become permanent.

Japan, which is most dependent on imported oil, spends very little on defense, a fact that is becoming increasingly annoying to some U.S. officials.

Yet U.S. defense planners do not envision any reconstructed Japanese military with a long reach. Rather, they want the Japanese to assume added navel, antisubmarine and air defense roles in Asia that would relieve the pressure on U.S. forces.

Just how nervous and uncertain allies are is reflected in the official silence from their governments about President Carter's State of the Union address Jan. 23, in which he announced one of the most important U.S. military shifts in postwar history: a commitment to defend the Persian Gulf region.

Though the president announced that it was "our position, he later acknowledged that it would require allied support to carry out. But there is no evidence that the president consulted the allies beforehand or that there have been any substantive discussions since about how this should be accomplished or how much these allies are willing to help.

Officials throughout the administration say that despite numerous trips abroad by Deputy Secretary of State Warren M. Christopher, discussions have tended to focus on such issues as the Olympic boycott, and that there never had been sufficient discussion to reach a common assessment of the threat, what to do about it, or Soviet intentions.

The United States evidently believes it is prudent to assume the Soviets are interested in the Persian Gulf and not just in Afghanistan. Many Europeans, believing the Soviets really began to take over Afghanistan in 1978, have not come to this view. Even some leading American commentators have warned against a U.S. overreaction.

The Europeans, more dependent on Middle East oil than is the United States, have more to lose than this country if relations with Moscow collapse. Not surprisingly they are not anxious to take any actions toward the Kremlin that would be irreversible. They are very worried by what they see as Carter administration inconsistency.

Europeans talk of a division of labor in which the French act in Africa of Iraq, West Germany helps Turkey and Pakistan, the British provide bases, and others provide access routes. Under this plan, the United States would do most of the fighting, though some U.S. officials believe that if the chips were down, Australian, British and possibly even French forces also would be engaged.

The crisis in the Persian Gulf region also highlights the shields that Western Europe and Japan can use to avoid taking dangerous and unpopular decisions or actions in which they have legitimate differences with Washington in their views and assessments.

NATO, for example, cannot take action outside the prescribed alliance region without breaking its charter. Even though Perisan Gulf oil is vital to many NATO nations, officials say there is no chance that NATO will expand its charter, a move that the French especially would oppose.

On the other hand, France has acted unilaterally with military force in Africa several times -- actions the United States supported on occasions when action by NATO would have been impossible.

West Germany and Japan both have constitutional limitations on the size and deployment of their armed forces. In the case of West Germany, U.S. officials say the German army and its reserves are too important to the defense of Europe to be shifted, although there are some who believe Bonn's sizable Baltic fleet could be moved around.