When President Reagan embraced the idea of a missile trade-off in Europe with the Russians Wednesday, he consciously gave his European partners in NATO a major victory in their campaign to gain a larger role in determining policy on nuclear weapons for the alliance.

The president may not have been aware, however, that he also was setting the stage for a new and severe conflict within NATO.

It is a conflict about leadership in the alliance that pits the United States, which traditionally has had its way on nuclear weapons policy in Europe during NATO's 31-year history, against the Europeans, who now want to move on to a key debate about the very future of battlefield weapons in their continent.

A move away from American domination of NATO nuclear policy has become necessary, one British defense official argued in an interview in London last month, "because the political futures of our governments have been hanging recently on offhand statements made by Amer- ican political and military men."

Reagan reassured those governments and handed them ammunition to use against Europe's growing disarmament campaigns by his endorsement Wednesday of their "zero option" negotiating posture, which his secretary of state had derided publicly in Europe only two months ago as "ludicrous." Getting the president's endorsement was the last element of a skillful orchestration by Europe of American decision-making on the NATO plan to deploy 572 Pershing II and cruise missiles in Western Europe.

Once deployed, the Pershing and cruise missiles will quickly become the anchor of NATO's deterrent nuclear force, according to European defense and political officials interviewed in Rome, London, Bonn, The Hague and Washington. They believe that a Euromissile force of even a few hundred warheads capable of hitting Moscow will represent a nuclear threat of more significance to the Soviets than the entire stockpile of 6,000 U.S. warheads now in Europe.

Arrival of these medium-range missiles will embolden the Europeans who would like to "clean out" the antiquated American short-range nuclear battlefield weapons before they become easy targets for the antinuclear protest movement.

"The next major debate within NATO is what place American nuclear weapons will have on Europe's battlefields," another British official said.

The forum for such a debate exists: the NATO subcommittee called the High-Level Group, which already has begun a review of the nuclear systems now in Europe and their need in the future given the proposal to introduce U.S. Pershing II and cruise missiles.

This review, known as the Shift Study, was requested by the Dutch government in 1979 as a quid-pro-quo that would enable The Hague to gain public support for introduction of cruise missiles. In return, the Dutch agreed to vote for Euromissile deployment.

For American officials, however, the Shift Study is an exercise with a limited goal -- picking out the 572 older warheads that the incoming new missiles would replace. Moreover, Pentagon planners, immune to the pressures of the hundreds of thousands of antinuclear marchers in Europe, continue working industriously on programs for more battlefield nuclear weapons and greater ease in using them in the Army's "integrated battlefield" doctrine, which enables NATO troops to switch back and forth between conventional and nuclear weapons on the battlefield.

This new American emphasis runs counter to the pressures developing on European officials, who say they are looking at the Shift Study as the device to review the need for nuclear short-range artillery, missiles and mines in the European stockpile.

Assistant Secretary of Defense Richard Perle is the current chairman of the High-Level Group, which is made up of top-level representatives from NATO country defense ministries and military staffs.

Members of the High-Level Group said they believe Perle will push on with the Shift Study now that the group's basic work leading to the adoption of the "zero option" negotiating position has been done.

The public protests against deployment of the new missiles has been accompanied by a sudden perception by Western Europeans that their countries are housing nuclear arsenals designed to be used on their own lands. Earlier this year, West Germany's largest magazine, Stern, published a map showing the locations throughout the country of American nuclear weapons and warhead stockpiles. It reportedly sold a record 19 million copies and the map became a popular wall poster.

Similar maps were then put together by newspapers and magazines in Britain, Greece, Italy and the Netherlands.

If the U.S.-Soviet talks on limiting medium-range missiles, which begin Nov. 30 in Geneva, drag on in the coming months, the peace marchers in West European countries are expected to turn their attention to the U.S. battlefield nuclear weapons, which are not the subject of any arms control talks.

A handful of key officials in NATO countries interviewed abroad emphasized the reinforcing nature of the Shift Study and the missile deployment. They argued that some major, well-publicized steps to cut that stockpile of battlefield warheads would help create the right political atmosphere to guarantee that the NATO missile deployment takes place as scheduled, beginning in December 1983.

NEUTRON WEAPONS

The Reagan administration's abruptly announced decision in August that it would manufacture and stockpile enhanced radiation warheads -- popularly known as neutron weapons -- is cited by Europeans as an example of American "mismanagement" of its policy on nuclear weapons intended for use in Europe that needs to be halted.

"Can you imagine that the Pentagon is threatening the deployment of a serious system the Pershing/cruise missiles to go ahead with this artillery shell that nobody knows how to use?" a British defense official asked in disbelief as he weighed the political costs of the neutron announcement against the Euromissile plan.

Although the Europeans have told Washington both publicly and privately that they see no possibility that eight-inch neutron artillery shells can be deployed in Europe, the Reagan administration is following through on its decision to build and assemble the controversial weapons.

In a concession to European sensitivities, however, the Reagan administration is stockpiling the shells in the United States and describes them as for use only by American forces. And although the Carter administration originally said that the neutron shells were to be designed specifically to meet the threat of Soviet tanks in Europe, Pentagon officials now say they are being produced for use anywhere in the world.

A second weapon, the 155mm nuclear artillery shell, is also being designed as a replacement for a 20-year-old warhead that is in the hands of American and NATO troops. It, too, was originally planned to be a neutron weapon. But designers were not able to reduce the neutron explosive charge -- which resembles a miniature hydrogen bomb -- enough to fit into the small artillery shell jacket.

The Pentagon is going ahead with a new 155mm nuclear shell with an explosive power that may be up to twice the size in the current one, which is less than one kiloton yield. The Pentagon has informally briefed European defense officials on this shell, which is years away from deployment, and the response has been ambiguous at best, according to NATO sources in The Hague.

WAR PLANNING

The real picture of the American desire to go on planning for a European nuclear war was given Sept. 15 by Deputy Under Secretary of Defense James P. Wade and Maj. Gen. Niles J. Fulwyler, director of the U.S. Army's nuclear and chemical directorate, during a closed hearing of the House Appropriations subcommittee on defense.

"A war-fighting capability is a fundamental and integral part of deterrence," Wade said, according to a declassified text of the hearing. "We don't want to fight a nuclear war or a conventional one either, but we must be prepared to do so if such a battle is to be deterred . . ."

Wade then went on to describe the Corps Support Weapons System, a new concept that "we envision . . . will be deployed later in the decade as a replacement for the current Lance 56-mile-range missile." The system would provide a "mobile Army surface-to-surface fire support system," which could deliver "nuclear, chemical and highly advanced conventional warheads on selected targets."

Wade also said the United States was looking into a new, nuclear antisubmarine weapon and was going ahead with development of a new ship-to-air nuclear missile, the SM2, which was specifically designed to meet the Soviet "Backfire-delivered cruise missile."

An American submarine-launched cruise missile, Wade said, was "nearing the end of its development." The option of deploying a sub-carried nuclear version in the European theater was still being studied in the Pentagon, in addition to the land-based Pershing II and cruise systems, whose deployment NATO had already approved.

Public discussion in Europe of such strategy would add enormous weight to the burden that West German Chancellor Helmut Schmidt and his counterparts in Belgium, the Netherlands, Scandinavia, and to a lesser extent Britain and Italy have to bear in getting their publics to support the Euromissile deployment.

The complicated and now apparently successful battle the Europeans have fought in getting American acceptance of the negotiating proposal that the Pershing and cruise deployment be cancelled in return for the Soviets dismantling their SS20s, SS4s and SS5s targeted on Western Europe -- the "zero option" -- is perhaps the clearest instance so far of the growing European determination to get more control over atomic affairs.

ALLIES' STRATEGY

Their strategy was based in part on their certitude that the Soviets will not accept the zero option. Schmidt in particular wants the missiles deployed, both to counter the ever increasing number of highly accurate SS20s the Russians are putting within striking range of West Germany and also to link the American nuclear deterrent even more tightly to West Germany's fate in the event of East-West war. If the Russians were to accept Reagan's version of the "zero option," the most chagrined leader in the world would probably be Schmidt.

But he has made it clear from the beginning of the missile deployment debate that such public gestures toward arms control were an absolutely necessary component of the missile package. That message was apparently hammered home to Secretary of State Alexander M. Haig Jr. on Sept. 13 by West German officials after he dismissed the notion of a zero option during a West German television interview. The following day, Haig pronounced the idea worthy of study.

British and other European sources now credit Defense Secretary Caspar Weinberger and Perle, however, with coming back from a swing to NATO capitals last month and converting Reagan to that approach.

NATO'S HALF TIME

Reagan's announcement comes at a symbolic half time for NATO, for it is two years since the deployment decision was made at a Brussels meeting and it is two years before the first missiles are scheduled to go on the ground.

As word of the new deployment idea became public in early 1979, the NATO governments were put under political fire. The first shots came from the Soviets, who immediately saw in the new systems a critical threat. In turn, groups of antinuclear, pacifist and procommunist activists joined in the antideployment effort.

The Netherlands, which had led the fight against the neutron weapons, became a center of opposition. Its government came up with the idea of trying to work out a substitute -- they would accept the new systems, whose warheads would land in the distant Soviet Union, in return for NATO taking out some of the short-range battlefield nuclear weapons already stored on Dutch soil. This was the origin of the Shift Study to determine just which of NATO's stockpiled warheads could be replaced with the arrival of the new longer-range systems.

The Americans also came up with the idea of adding a reduction of 1,000 warheads already in the stockpile to the deployment package as a sweetener for the Dutch and others who had to have something to offer their antinuclear constituencies.

But the major part of the package originated with the West Germans. It was the idea that while NATO awaited deployment of the new missiles, it would offer to negotiate their numbers with the Soviet Union in return for some limits on the SS20s, SS4s and SS5s.

"The Pershings," an adviser to Schmidt said recently, "was a certain stick and with negotiations we tried to do the carrot."

The so-called two-track notion had its effect on stretching out from December 1983 through 1988 the deployment of the systems. The hope within NATO was that somewhere before the deployment of all the planned 572 missiles -- perhaps around 300 -- some agreement could be reached with the Soviets.

The British accepted 160 cruise missiles, but did it in two batches. The first 96 would begin coming in December 1983 as the first deployments; but the final 64, scheduled to be placed at a second base, would not begin to arrive until the very end of the deployment near 1988 -- the obvious hope being that the British might not have to take the second group.

The West Germans are in the same game. They will take the 108 Pershing IIs as an early deployment in 1984, but their planned 96 cruise missiles are not scheduled to arrive until after similar missiles go into Italy, Belgium and possibly the Netherlands.

As the alliance headed toward a December 1979 decision date, Schmidt made one final gesture to his critics, asking the High-Level Group to take another look at the less provocative submarine-launched cruise missiles option. It was quickly turned down, but not before causing anger and tension in Washington toward the West German chancellor.

Other European political imperatives were also at work. The Italian government, embarrassed by being left out of the four-power summit meeting in Guadeloupe in January 1979 and deeply concerned about emerging indications that France and Britain were close to reviving the idea of a "directorate" within the Common Market that would also exclude Italy, chose the missile issue as their way back into the ranks of acknowledged leadership.

Acting, in the thought of one Italian official at least, in a way to show NATO that Italy would not agree to be downgraded to the status of a Portugal or a Norway, the Italians assured Schmidt in October that they would accept the missiles.

The Dutch, despite U.S. agreement to the "shift study," delayed a final decision until December 1981 -- a date that already has been postponed again amidst clear indications that no Hague government may be able to get approval for the 48 missiles earmarked for the Netherlands. Belgium, too, has postponed a final decision on its 48 missiles..

The Dutch and Belgians will be closely watching the next key decision date for the missile deployment -- the April 1982 national party conference of Schmidt's Social Democratic Party in West Germany. Schmidt has indicated that he would quit if the party does not endorse his two-track policy on the missiles.

West German officials delightedly point out that the prospect of the missile deployment taking place on schedule has already brought the Russians to the negotiating table on theater weapons.

SOVIET REJECTION

In October 1979, Soviet President Leonid Brezhnev said that if the deployment decision was taken, the Soviets would never negotiate with NATO on the SS20s. But if NATO turned down the new missiles, the Soviets would freeze the SS20s at their 1979 level.

In July, 1980, Schmidt went to Moscow, and the Soviets began to suggest that they were prepared to negotiate on theater nuclear forces and in October 1980, Soviet and American delegations sat down for one month of talks on limiting theater nuclear weapons.

Schmidt is now apparently embarked on an even more audacious gambit, even though his spokesmen continue to insist that West Germany does not want to be a mediator between the two superpowers. He will discuss the issues with Brezhnev in Bonn beginning Sunday, and he will then see Reagan in Washington on Jan. 5.

It is far from clear at this point where the European bid for management of theater nuclear weapons will go next. But there is a mood among some Europeans now to turn to a new look in the NATO nuclear deterrent, one based more on a French-style, force de frappe, made up of about 1,000, rather than 6,000, U.S. nuclear warheads from artillery through longer-range Euromissiles.

The fewer numbers, European sources insist, would mean that the NATO force would act more as a trigger for the American strategic ICBM force, and less as a weapons base designed to fight a full-scale nuclear war limited to Europe.

In a recent analysis published by the International Institute for Strategic Studies, Gregory Treverton, the institute's deputy director, and former member of the Carter administation's National Security Council staff, argued, "It is hard to conceive of why NATO should have anywhere near the number of short-range and battlefield nuclear systems it now possesses."

But, Treverton went on to acknowledge that nuclear weapons have traditionally been used to make up for imbalance of NATO conventional forces against the Warsaw Pact and "it will be difficult to wean some parts of the NATO military establishment -- notably the American Army -- away from them."