Soviet Foreign Ministry spokesman Gennadi Gerasimov, hinting at a major arms concession by the Soviet Union, suggested yesterday that his government might drop its longstanding demand that the United States accept formal restrictions on space testing of a ballistic missile defense.

Gerasimov's suggestion was that the two nuclear superpowers simply agree to continue adhering to the 1972 Antiballistic Missile (ABM) Treaty as a basis for dealing with the hotly contested strategic defense issue, without spelling out what the treaty means. Such a move would skirt the issue of what is permitted and what is prohibited under the treaty, which has been at the core of the argument between the two nations over strategic defense.

If Soviet leader Mikhail Gorbachev offers such a position in talks with President Reagan here next week, it could ease the way for early agreement on deep cuts in strategic, or long-range, offensive arms.

The first step toward nuclear cutbacks is to be taken by Reagan and Gorbachev Tuesday when they sign a treaty eliminating U.S. and Soviet medium- and shorter-range nuclear missiles. They will devote much of the three-day summit to bargaining over how to achieve their stated goal of deep reductions in long-range strategic nuclear weapons.

Gerasimov's remarks echoed other, private comments this week from visiting Soviet diplomatic officials and arms-control experts who said Moscow is less worried than in the past that Reagan's Strategic Defense Initiative (SDI) research plan will lead to a space-based defensive system that would be truly effective against Soviet missiles. Several of these visiting Soviets said Moscow now thinks that Reagan's vision of a shield in space against incoming missiles is a dream that cannot be fufilled.

A Monday statement on SDI by Gorbachev appeared to leave room for the position suggested by Gerasimov.

"We shall be talking about strict compliance with the ABM Treaty," Gorbachev said in an interview telecast by NBC. "The question of SDI is not a subject for the negotiations."

However, the exact Soviet position on SDI research remained unclear, because a senior Soviet military arms-control expert offered a formulation different from that expressed by Gerasimov and other Soviets in the summit delegation who agreed with him. Gerasimov's remarks were made at a breakfast sponsored by World Paper, a newspaper supplement.

Col. Gen. Nikolai Chervov, chief of the arms control section of the Soviet General Staff, said in an interview with The Washington Post yesterday that his personal view is that the United States and the Soviet Union should solve their dispute over space defenses by agreeing to observe the ABM Treaty "as it was signed and ratified in 1972."

This language has been interpreted by the Soviets as referring to a restrictive or "narrow" view of the ABM Treaty barring realistic space tests, a view that was held by the United States from 1972 until 1985. The administration has insisted since then that this traditional view is not correct.

Nevertheless, Reagan yesterday grudgingly signed into law a defense bill that bars spending for tests that would violate the traditional interpretation of the treaty. Reagan signed the bill on a day when he held a final meeting with his senior arms control and foreign policy advisers on the positions to be taken in next week's talks with Gorbachev.

Senior U.S. officials said yesterday it is unlikely that Reagan will agree to a proposal by Gorbachev that both sides abide by the ABM Treaty "as it was signed and ratified," because it is so clearly understood to be a euphemism for the restrictive interpretation.

But several officials also expressed reservations about Gerasimov's more flexible formula. Leaving the issue unresolved, they said, could enable the Soviet Union to pursue whatever missile defense testing it desired, even though Congress might block similar U.S. tests.

Although the Soviets have long insisted that limits on SDI are a key to reductions of strategic nuclear arms, Moscow's position on such limitations has been evolving the past two years toward greater flexibility.

Chervov's remarks echoed the most recent formal Soviet proposal advanced here in September that the two sides adhere to the ABM Treaty "as it was signed and ratified." An alternative Soviet plan, which Chervov strongly endorsed yesterday, called for the two sides to agree on a list of permitted space tests.

The administration has rejected this "list proposal," and Gerasimov said "we are not pressing it." Gerasimov said "the best result" of the summit meeting would be for Reagan and Gorbachev to agree on "guidelines" or instructions to their negotiating teams on the details of a strategic arms treaty "including the mention of the ABM Treaty."

Gerasimov said "we are simply saying, let us repeat that we are going to abide by this ABM Treaty, which is a good treaty." He added, "What is the point of a quarrel? There is no quarrel there."

Gerasimov said the United States and the Soviet Union do not need to discuss the correct interpretation of the ABM Treaty, partly because Congress has already taken action to require the administration to abide by the restrictive view for the next year.

"In my view, if we have good progress on strategic arms, this particular issue is going to fade away," he said.

Chervov said, "I'm not a supporter of the narrow or of the broad interpretation." He said the only reasonable approach was to interpret the treaty "as it was signed and ratified," and that lawyers and "quacks" claiming to interpret it have only added to discord and confusion.

On a related issue, Chervov said an administration accusation this week that movement of some Soviet radar equipment violates the ABM Treaty can be soon cleared up by a U.S. team that will visit the radars at Moscow and Gomel, north of Kiev, on Dec. 14-16 at Soviet invitation.

A senior State Department official said last night, however, that while "the general framework for the visit is agreed," the proposal had not been formally accepted.

Chervov also indicated that the Soviet Union would be flexible on other major arms control disputes, including how long the superpowers would agree to abide by the ABM Treaty.

The Soviet Union has sought a 10-year U.S. commitment to the treaty, because it would put off for a decade any U.S. missile defense deployment in space. The Reagan administration has said it will commit to the treaty for another seven years or through the end of 1994.

Finally, Chervov and Gerasimov said the two sides are likely to resolve another dispute over how to set limits on strategic missiles. The United States has sought deep cuts in Soviet land-based missiles, while the Soviets have sought greater limits on U.S. submarine-based missiles than the Reagan administration has been willing to accept.