REYKJAVIK, ICELAND, JUNE 11 -- The NATO allies have agreed to back a U.S.-Soviet accord to remove medium- and shorter-range nuclear missiles from Europe and are paving the way for France to rejoin alliance consultations on arms control, U.S. officials said tonight.

The allied "consensus," which is to be formally announced in a NATO communique Friday, will provide a much-awaited signal for the United States to accept Soviet leader Mikhail Gorbachev's offer to remove two classes of missiles -- those of a 300-600 mile range and those that can fly 600-3,500 miles -- which have been the focus of six years of negotiations.

Officials said President Reagan, armed with the allied approval, plans to announce new instructions to U.S. negotiators in Geneva on Monday in a drive toward early completion of the first U.S.-Soviet treaty of his administration and a summit meeting in Washington with Gorbachev to sign it later this year.

The allied approval of the "zero-zero" formula, calling for removal of all of the missiles in the two classes, had been expected since the West German government, the last important holdout, had agreed to endorse it last week.

The possibility of France rejoining NATO consultations on arms control negotiations with the Soviet Union was unexpected. A State Department official who briefed reporters suggested that the initiative had come from Paris because of the "dramatic change" in the arms control agenda following the Reagan-Gorbachev talks held in this city eight months ago.

U.S. and French negotiators have drafted language about future arms negotiations that would permit the French to rejoin the NATO consultations after what has been a 20-year absence, reporters were told. They have submitted their draft to the governments in Washington and Paris and to allied foreign ministers here, reporters were told. If approved, the language will be made public here Friday.

The accord will not bring France back into the military structure of NATO, which it left in 1967, nor will it give Paris a veto or other decision-making authority over future U.S.-Soviet negotiations, according to the U.S. sources. But it will broaden allied consultations on future negotiating moves and thus provide the possibility of more unified western positions.

France along with Britain has independent nuclear forces that could be affected by arms control developments, although Washington has insisted on excluding them from the talks with Moscow on the medium-range missiles. France also has been taking a major role among European nations in bilateral discussions with the Soviet Union; Paris hosted Gorbachev's first trip to the West after he became the leader of the U.S.S.R.

A dispute, between the France on the one hand and the United States and most of the NATO allies on the other, over a forum for negotiating reductions in conventional forces in Europe was the focus of intensive discussions here tonight, with the prospect appearing to be good that it can be resolved.

The French have been asking that the 35-nation Conference on Security and Cooperation in Europe, which includes neutral nations, have a role in a new set of expanded negotiations to reduce land armies in Europe. The United States and most of its allies have wished to limit the negotiations to the 16 members of NATO and the seven members of the Soviet-led Warsaw Pact.

A NATO committee was meeting tonight in an attempt to forge a compromise that will permit the Atlantic alliance to approve new negotiations with the Warsaw Pact on reducing land armies "from the Atlantic to the Urals." Gorbachev proposed such negotiations in a speech in East Berlin 14 months ago.

Still another problem before the alliance appears to have been solved in today's discussions among the NATO foreign ministers, including Secretary of State George P. Shultz. A draft of Friday's NATO statement will list cutbacks in battlefield nuclear weapons, those with a range of less than 300 miles, as a subject for future negotiations, but will not give it any special urgency or priority, officials said. This appears to satisfy both Washington and Bonn.

West German authorities have been urging that the alliance move promptly toward cutbacks in these battlefield, or tactical, weapons, which are on German soil. But the United States is wary of such negotiations because of concern that they would suggest "denuclearization" of Europe at a time when the Soviet Union maintains the edge in nonnuclear forces.

Addressing the formal opening session of the NATO foreign ministers' meeting this morning, NATO Secretary General Lord Carrington called on the allies to develop "a new degree of tactical flexibility" in dealing with a seemingly more flexible Soviet leadership. Carrington said recent NATO studies clearly indicate that Gorbachev "is neither a revolutionary nor a counterrevolutionary, but he is a reformer who by slow degrees is opening up the Soviet Union to the outside world." Carrington added that this "offers a greater hope of positively influencing developments within the Soviet Union where such a possibility barely existed in the past."

At the same time, Carrington called for NATO to keep up its vigilance and its defense expenditures, saying that the Soviet Union is continuing to expand and upgrade its nonnuclear military forces in Europe. He noted that last month, the NATO defense ministers had expressed concern about "a widening gap between the capabilities of NATO and Warsaw Pact forces".

Shultz has not requested allied help for U.S. efforts to defend Persian Gulf shipping, a spokesman said.