When North Atlantic Treaty Organization leaders decided at their recent London summit to start trimming NATO's defenses, the prospect of fewer American soldiers and weapons in Europe seemed to promise smaller bills for U.S. taxpayers.

Eventually things should turn out that way. But it will take time to work through all the strategy reviews, arms-control negotiations and other issues involved in turning NATO into a stripped-down military machine. The immediate future promises no quick end to the tensions over what the 16 NATO members euphemistically call "burden sharing."

That is the international equivalent of 16 people poring over a dinner check and squabbling about who should pay what. Many Americans are convinced that the prosperous Europeans have not paid their fair share of NATO's costs, instead letting the United States pick up most of the tab.

Many members of Congress, including Senate Armed Services Committee Chairman Sam Nunn (D-Ga.) and Rep. Patricia Schroeder (D-Colo.), an influential House liberal, have warned that the United States no longer can afford to make what they contend is a contribution to NATO of $160 billion annually. They want the dramatically reduced tensions of post-Cold War Europe to be matched by substantial cuts in U.S. defense spending.

Intense congressional pressure compelled President Ronald Reagan in 1988 to make the Europeans agree to seek a more equitable distribution of NATO's costs. Last year, veteran State Department diplomat H. Allen Holmes was named to the new post of special ambassador for burden-sharing.

But Holmes had barely taken office when the political revolution in Eastern Europe brought down the Berlin Wall, plunged the Soviet Union into internal political and economic crises and derailed the Warsaw Pact.

The post-Cold War era promises a smaller, leaner, cheaper NATO. But the issue of who pays -- and how much -- won't disappear.

In addition, high costs loom ahead to pay for what a NATO official calls "the problems of detoxifying a Europe contaminated by more than 40 years of military confrontation." These costs will include environmental cleanup, closing unneeded bases, getting rid of excess arms and equipment, and redistributing what remains.

Holmes and other U.S. officials say it is too early to estimate the U.S. share of NATO's future costs. He and other administration officials say members of Congress are incorrect to peg current U.S. NATO costs at $160 billion, arguing that the figure includes many costs U.S. armed forces would incur even if the United States were not in NATO.

Administration officials say NATO members have agreed that any future arms reduction treaties should allow the United States to reduce manpower and equipment faster and in greater degree than European members, bringing a dramatic and swift tumble in the cost of the U.S. commitment.

But there is a still a big gap between what the administration and Congress want U.S. cuts to be. President Bush and Secretary of State James A. Baker III took the lead in drawing the blueprint for a stripped-down NATO, but they also argue that U.S. forces in central Europe, now roughly 336,000, should not be reduced below 195,000.

Nunn calls that "no longer realistic," and favors cutting back to 75,000 to 100,000 within five years. Arguing that it would take months for the Soviets to launch a conventional forces attack against NATO, Nunn contends that the bulk of U.S. troops could stay home and go to Europe only in an emergency. Schroeder, who heads the House Armed Services subcommittee on military installations, agrees that most U.S. forces should be based here and "deployed only for short-term training exercises at bare-boned bases in Europe."

Burden-sharing involves two areas of cooperation. Member countries make direct contributions to the defense structure under NATO's unified command. The bigger, more powerful members such as West Germany and Britain deploy troops alongside U.S. forces confronting Soviet forces, while smaller, poorer NATO states, such as Iceland, Spain and Greece, contribute by allowing U.S. planes and ships to operate from bases within their territory.

There also are "host country offset arrangements" such as free facilities or absorbing some U.S. expenses to help defray costs of a large U.S. military presence within a member's borders.

The most far-reaching and costly of these agreements is with West Germany, where most U.S. troops in Europe are stationed. Over the years, working out U.S.-West German offset arrangements has been accompanied by wrangling that former West German chancellor Helmut Schmidt called "a tug of war where we pay more than we want to and less than the Americans want us to."

U.S. and West German officials say it is impossible to accurately gauge the total value of Bonn's support for the 400,000 allied troops and 200,000 dependents -- three-quarters of them Americans -- in West Germany. But it includes land and base facilities with a real estate value of $28 billion and an annual rental value of $800 million, $500 million a year for upkeep of allied forces in Berlin, $366 million to maintain the readiness of 93,000 West German reservists to support U.S. troops in a war emergency and $120 million a year to pay for damages caused by U.S. forces to private German property during maneuvers.

The collapse last fall of the communist regime in East Germany has given burden-sharing a bizarre new twist, with West Germany offering to pay up to $550 million a year toward keeping Soviet troops in a unified Germany for five years. In fact, the economic union of the two Germanys that is replacing the East German mark with West German currency already has required Bonn to start giving the Soviets large sums in West marks to cover East Germany's $750 million annual payment to maintain Soviet forces on its territory.

The West German payments underscore how much has changed since a year ago, when NATO defense ministers were worrying about meeting the alliance goal of a 3 percent real increase in each member's annual defense budget. Now they are wondering how soon they will be able to adopt as official NATO policy a plan for cuts in defense spending.

The answer hinges on the NATO strategy review and two other diplomatic initiatives -- the conventional forces in Europe (CFE) reduction negotiations in Vienna, and the two-plus-four talks on German unification.

The CFE process aims at agreement by year's end to bring NATO and Warsaw Pact members down to a common ceiling on troops and conventional weapons. The German unity talks, involving the two Germanys and the four principal World War II victors -- the United States, the Soviet Union, Britain and France -- probably will determine how many German and foreign troops will be deployed in the old central front that formed the NATO-Warsaw Pact front lines.

Once the agreements are made, said a U.S. official, "There obviously will be a big reduction of our presence in places like Germany." He said German federal and state officials already are "hinting that they'd like to get back the airfields and other valuable real estate that the United States has controlled for 45 years. And right behind them we've got another group of German officials at the local level coming in and saying, 'Please don't close your bases too fast. It would cause disastrous unemployment and economic hardship for our towns.' These are all problems that will have to be addressed, but it's still too early for that."

Instead, Holmes and other NATO officials are focusing on the more immediate problems of how to distribute the costs of paring NATO forces.

The CFE agreement calls for extensive NATO and Warsaw Pact verifications of compliance with base closings, destruction of weapons and other equipment and limitations on military maneuvers.

This will be "a costly, very labor-intensive effort," said a U.S. official, who added that the allies are working out the formulas for how much money and personnel each member should contribute.

In addition, NATO faces special costs in destroying old weapons and distributing surplus advanced equipment to poorer members, such as Turkey and Greece, from stockpiles in the richer countries. "That will require a very expensive effort of sorting, inventorying, repackaging and shipping the equipment within the alliance. Again there has to be a formula for apportioning the work and the costs."

Finally, the alliance may work out a plan for turning over many of its airfields, air traffic control centers, fuel pipelines and other facilities to private companies, with the understanding that NATO could reclaim them in a war emergency.

Administration assurances that the distribution of costs will be equitable to the United States draw a skeptical response from Schroeder, who recounted how the United States recently gave up the huge Torrejon air base near Madrid under pressure from the Spanish.

"We were thrown out, but we wound up agreeing to pay for the cleanup, the severance pay to local Spanish workers and millions {of dollars} in other costs," she said. "We have to make clear to the Europeans that they can't look to us as the deep pockets any longer and that what we want are understandings that will allow us to draw down our forces in Europe quickly. Otherwise I think Congress will decree that we pull back regardless of whether we've reached all the agreements the administration wants."