The western allies unveiled a new proposal for troop reductions in Central Europe today that seeks to break the deadlock over East-West talks on conventional force levels by adopting a framework suggested by the Warsaw Pact.

In the first arms control initiative since the Geneva summit, North Atlantic Treaty Organization representatives said they had made a "significant concession" by dropping their demand for prior agreement on the size of Soviet Bloc forces stationed in the region.

The Vienna negotiations, known as the Talks on Mutual and Balanced Force Reductions in Europe, or MBFR, have languished for most of their 12 years because of a protracted dispute over troop numbers. The West claims that the East underestimates its forces by 230,000 men.

Acting on what he called the "major political impulse" of the Geneva summit, chief U.S. delegate Robert Blackwill said the 12 NATO participants wanted to test Soviet Bloc promises of substantial progress once the "data barrier" could be broken. By abandoning its previous stance and moving toward the Warsaw Pact's approach, the West has "brought the talks to a decisive crossroads," Blackwill said.

The western proposal embraces the East's concept of a first-phase reduction involving U.S. and Soviet forces, following by a "no increase" commitment by both alliances for the next three years.

Last February the Warsaw Pact proposed opening cuts of 20,000 Soviet troops and 13,000 Americans as well as a ceiling on soldiers currently deployed by both alliances. The new western version accepts this format but prescribes a smaller initial withdrawal of 11,500 Soviet troops and 5,000 Americans.

[In Washington, President Reagan said the NATO proposal was conditioned on Warsaw Pact acceptance of an "effective package of verification measures" that "is intended to verify the numbers of troops withdrawn as well as the numbers which will remain." State Department spokesman Bernard Kalb said that the proposal included the exchange of information "on forces in the area, broken down to battalion level, including specific locations," and that on-site inspection time under the proposal was "three times" that called for in previous NATO proposals.]

British Prime Minister Margaret Thatcher and West German Chancellor Helmut Kohl have persisted for months in urging a dramatic new western proposal at the MBFR talks, according to senior western diplomats. Both leaders used their good rapport with Reagan to coax American support for significant changes in the West's position, the diplomats said.

The new proposal quickly acquired widespread support among NATO governments because of the belief that bolder, more imaginative steps were necessary to restore public faith in arms control and to recapture the initiative from Moscow after a spate of Soviet offers to freeze or reduce nuclear arms testing and development.

The troop cut proposal "sailed through NATO in record time once the summit concentrated everyone's minds," a western diplomat said. "It is hard to believe we would have gotten one before Christmas without the summit."

British Ambassador Michael Alexander declared today that the NATO countries now had adapted their position to such an extent that they had established 16 areas of agreement with the Warsaw Pact over how to bring about a treaty on troop cuts in Europe. He said that the West's latest offer will help enormously in overcoming many years of "a dialogue of the deaf."

Despite the narrowing of key differences on early troop withdrawals and a ceiling on bloc forces, the negotiating positions between the East and West remain in sharp conflict over whether to reduce the quantity of armaments and over ways to verify that lower troop levels are being respected.

Chief Soviet delegate Valerian Mikhailov, responding to the western offer put forward at the close of the negotiating round today, said that even though western countries seemed formally to accept the East's approach, "they filled it with dubious content."

The seven Warsaw Pact nations, anxious about NATO's arms modernization plan, have demanded that all troops being removed should take away their weapons and combat equipment. The West says that each side "should have the discretion to decide for itself" on how to dispose of its weapons and calls a ceiling on armaments "neither meaningful nor practicable."

NATO also insists on permanently manned entry and exit posts for all forces to pass through, as well as the right for each side to conduct 30 on-site inspections a year during the three-year interim phase. The Soviet Bloc countries have rejected such rigorous inspection procedures in the past as too intrusive and have called for any troop agreement to be honored by "political good will" and monitored by existing reconnaissance systems.

Mikhailov contended that the NATO offer "bears the longstanding vice of their stance" toward verification and an arms ceiling.

The Soviet ambassador said the NATO countries "stubbornly eviscerate everything that could lead to an actual reduction in the level of military confrontation in Europe; for instance, reduction and limitation of armaments." He added that the West is also trying to "impose excessively inflated verification measures disregarding existing realities."

While noting that the proposal "does not give cause for optimism," Mikhailov said that the points included in the western offer would be "carefully studied as to what extent they can facilitate overcoming the deadlock in reaching a concrete result at the talks."