U.S. officials said yesterday that the administration has decided, after protracted negotiations, to bow to Spain's demands and withdraw 72 U.S. fighter jets from a base there.

The move is the first unilateral reduction of U.S. forces ordered by a European ally since France closed bases in 1966 and withdrew militarily from the North Atlantic Treaty Organization (NATO).

Early last month Spanish Prime Minister Felipe Gonzalez broke off negotiations and said the three F16 squadrons that make up the 401st Tactical Fighter Wing must be withdrawn within 3 1/2 years.

A well-informed administration official said "the deal is wrapped up."

He said that in exchange for withdrawing the jets, the United States obtained some concessions from the Spanish on issues he refused to specify.

He said an outline of the agreement will be announced "very soon," and that details of the accord are still being worked out.

Under NATO plans, in times of crisis the jets, capable of carrying conventional or nuclear weapons, are to be sent to bases in Italy and Turkey to help defend against Soviet invasion.

Belgium, Portugal and Morocco have reportedly expressed interest in accepting some or all of the F16s. About 4,500 U.S. airmen are attached to the air wing.

In its recent approval of the defense budget, Congress barred the Defense Department from paying for any new base for the planes. The move was aimed at forcing NATO allies to deal with the problem of U.S. forces.

U.S. officials are concerned about the effect of the move on efforts to reach new basing agreements in Greece and the Philippines and to resolve disputes with Turkey and Portugal over existing defense accords.

Gonzalez has said he does not want to disturb other U.S. installations in Spain and plans to sign a new accord covering them when the current one expires in May.

Meanwhile, President Reagan has made tentative plans to attend a March or April meeting of the heads of state in NATO, where he intends to reassure them that the United States remains committed to the defense of Western Europe.

The rare NATO summit meeting, which British Prime Minister Margaret Thatcher urged on Wednesday, is also expected to give the allies an opportunity to express views on arms control and East-West relations before Reagan visits Moscow in May or June for a summit with Soviet leader Mikhail Gorbachev that is intended to center on strategic nuclear arms reductions.

Concern among many European allies about U.S. military support may have been exacerbated by a speech in Washington Wednesday by Secretary of the Navy James H. Webb Jr., in which he called for a reevaluation of force deployments around the globe.

White House and Pentagon officials took pains to distance themselves from Webb's remarks yesterday in an effort to avoid antagonizing European leaders, who have supported the new U.S.-Soviet pact to eliminate land-based nuclear missiles in Europe, but expressed anxiety about any further U.S. arms reductions there.

Webb, in a speech to the National Press Club, said the United States should reassess its force structure in Europe and elsewhere because of shrinking defense budgets and increasing Soviet influence in other regions. "We must remain strong in Europe," Webb said, but added, "We have a requirement, contrary to European nations, to view the Soviet military threat in Europe through more than a European prism and to be fair to the other areas in which we must operate."

Webb said U.S. policymakers should begin emphasizing defenses in Asia and Latin America, for example, and added that budget restraints could force a U.S. conventional force reduction in Europe.

Secretary of State George P. Shultz reportedly "was livid" over Webb's comments, according to one administration source. Defense Department spokesman Fred S. Hoffman said yesterday, "Webb was expressing his own views, not the views of the {Defense} Department."

A spokesman for Webb said the Navy secretary had not intended to "antagonize or embarrass our allies, but to bring into focus present-day realities we will have to face for the next 10 to 20 years."

Meanwhile, U.S. and Soviet negotiators began their ninth round of talks in Geneva yesterday on a treaty limiting strategic nuclear weapons.

Reagan said in a written statement an agreement "can be reached this year, if the Soviets return to Geneva ready to apply themselves with the same seriousness as the United States." But he added that "important differences remain."

Reagan reiterated his position that the Strategic Defense Initiative (SDI), which the Soviets want to restrict, "is not a bargaining chip."

Chief Soviet negotiator Alexei Obukhov this week restated Moscow's position, however, that no cut in strategic arms is possible without a U.S. commitment to adhere to the traditional interpretation of the 1972 Antiballistic Missile Treaty, which bars the realistic SDI space tests that interest Reagan.

Meanwhile, White House spokesman Marlin Fitzwater said Reagan was feeling fine after experiencing vomiting and nausea Tuesday night. The president plans to enter Bethesda naval hospital for a semiannual cancer checkup this afternoon.

Staff writers Molly Moore and Bill McAllister contributed to this report.