REYKJAVIK, ICELAND, JUNE 12 -- The NATO alliance today formally approved elimination of two classes of medium-range nuclear missiles from Europe and, in a surprise move, authorized a new set of East-West negotiations on reducing the massive armies on the divided continent.

The start of expanded negotiations on cutbacks in NATO and Warsaw Pact land forces had been hung up for more than a year by procedural disputes between the United States and France. Officials of the two nations said the impasse had been broken by conversations in Venice this week involving President Reagan, Secretary of State George P. Shultz and French Prime Minister Jacques Chirac, plus other discussions here and in Paris.

NATO's approval means the new East-West talks on conventional forces "from the Atlantic to the Urals" are likely to begin formally in the early or middle part of next year, U.S. officials said. The new talks will supersede the 13-year-old Mutual and Balanced Force Reduction negotiations in Vienna, which have not been successful.

NATO's endorsement came two months after Soviet leader Mikhail Gorbachev proposed eliminating a medium-range class of missiles capable of striking targets between 300 and 600 miles away. The United States has long insisted that the two sides must have equal numbers of such missiles as part of any agreement to remove from Europe a larger category of medium-range missiles, those with a range of 600 to 3,500 miles.

Secretary of State Shultz, who received Gorbachev's proposal in an April meeting in Moscow, was favorable from the outset because, of the superpowers, only the Soviets now deploy the shorter-range class of missiles, which it will eliminate with no corresponding western reductions. Still, Shultz deferred making an immediate official answer pending consultations with the European allies.

Gorbachev's April offer paralleled the U.S.-proposed "zero option" of 1981, providing for elimination of all medium-range, or so-called theater nuclear missiles.

{The Soviet news agency Tass called the NATO move "a first but very timid step toward disarmament," and said the alliance's failure to approve elimination of 72 shorter-range German Pershing IA missiles threatened "to complicate and slow down" any overall agreement, Reuter reported from Moscow.}

NATO Secretary General Lord Carrington, who called the NATO action "a full allied endorsement" of the U.S. position in its Geneva talks with the Soviets, said, "I think we can foresee removal from Europe and perhaps the global elimination" of both classes of medium-range missiles.

Shultz called the NATO action "a very clear consensus" that Reagan can take into account in issuing instructions to U.S. negotiators in Geneva. U.S. officials here said they expect Reagan to accept Gorbachev's April offer within the next several days and to announce his stand in a televised address scheduled for Monday.

Officials said that many details remain to be settled at Geneva but that prospects are now good for the first U.S.-Soviet treaty of the Reagan administration and a Reagan-Gorbachev summit meeting in Washington later this year.

The NATO communique continued to urge the Soviet Union to eliminate all of the longer-range missiles, rather than to retain 100 warheads in Asia and permit the United States to retain 100 warheads on its territory. Reagan agreed at his meeting with Gorbachev here in Reykjavik last October to accept the retention of 100 warheads on each side even though the United States prefers a total ban.

Acceptance of the Soviet offer on the shorter-range missiles has been a contentious issue within the NATO alliance, mainly because of concern that it could represent the start of an unstoppable trend toward "denuclearization" of Europe while the Soviet Union continues to hold the edge in nonnuclear forces.

Today's NATO statement, made public at the end of a two-day meeting of the foreign ministers of the 16 member nations, reaffirmed the strategy of "deterrence" based on nuclear as well as conventional forces. In this respect the U.S. nuclear commitment and the presence of U.S. nuclear forces in Europe "remain essential," the NATO statement said.

West Germany's insistence that the allies not close the door to reducing battlefield nuclear weapons in the range below 300 miles was accommodated by listing such cutbacks among arms control questions to be studied by NATO. There was no commitment to undertake such cuts and U.S. officials said they are unlikely, but West German Foreign Minister Hans-Dietrich Genscher said he was satisfied by the outcome.

Another West German concern, the German Pershing IA missiles whose warheads are controlled by the United States, was not mentioned in the NATO communique. Both Carrington and Shultz insisted, however, that these weapons should not be included in U.S.-Soviet bargaining. The remarks suggested that the West will be adamant on this issue, which has only recently been raised by Moscow.

The arrangement between the United States and France that eliminated the barrier to new conventional arms negotiations was described by U.S. officials as also a factor in the French decision to take a greater consultative role in arms control issues before the Atlantic alliance.

The new role was signified by a paragraph in the NATO communique that did not, as in the past, clearly exclude France from consideration of future developments in the U.S.-Soviet talks on missiles in Europe. French Foreign Minister Jean-Bernard Raimond, in a separate news conference, minimized the change in France's consultative role on arms control policy.

Raimond, in an account confirmed by U.S. officials, said Prime Minister Chirac had made clear to Reagan in Washington in March French insistence that new East-West negotiations on conventional forces be linked to the 35-nation Conference on Security and Cooperation in Europe (CSCE). The United States had maintained that only the 23 nations of NATO and the Warsaw Pact should be included.

Shultz and Raimond reached basic agreement yesterday that the new negotiations on conventional force reductions will be an autonomous bargaining effort of the 23 NATO and Warsaw Pact nations "within the framework" of the 35-nation CSCE process. A U.S. official called this "an optical cover" for France, but the French minister described the link as very significant.

A detailed paper stating how the new negotiations are to work was hammered out by U.S. and French officials here, endorsed by the two home governments and a high-level NATO committee last night and approved by the NATO ministers this morning.