A senior Soviet official warned West Germany today that its participation in President Reagan's "Star Wars" research project for space-based missile defense could undermine the Anti-Ballistic Missile treaty and damage chances for successful results at the summit in Geneva.

Vadim Zagladin, deputy head of the Central Committee's international affairs section and one of Moscow's leading spokesmen on East-West issues, said at a press conference that Bonn's intention to sign an agreement with Washington ensuring an exchange of research findings would conflict with treaty provisions forbidding the United States and Soviet Union from sharing ABM technologies with other states.

The warning, following a toughly worded letter recently sent by Soviet leader Mikhail Gorbachev to Chancellor Helmut Kohl, appeared to escalate the Soviet campaign to erode West German backing for Reagan's Strategic Defense Initiative. Diplomats said it was the first time they could recall a top Soviet official publicly admonishing the American ally about becoming "an accomplice" in breaking the ABM treaty.

In his letter, Gorbachev noted that the Bonn government had given the Strategic Defense Initiative "active political support" and was now arranging conditions for West German companies to join "American programs which have as their goal the creation of space strike systems."

The Soviet leader argued that the Kohl government faced a dilemma of "whether it allow the material, scientific and technological potential of its country to be used for the realization of the most dangerous military plans in space, or whether it will assert its reputation and influence in order to contribute to bringing about mutually acceptable agreements."

"We make out judgments about political intentions on the basis of actual deeds," Gorbachev wrote. "I would like to hope that your government will act in awareness of the responsibility it has taken upon itself, and toward its own and other peoples."

The Gorbachev message appeared in its entirety in the mass circulation daily Bild Zeitung, infuriating Kohl and prompting charges that the Soviet Embassy had leaked the letter to embarrass the Bonn government and to exploit lingering doubts about its role in U.S.-led missile defense research.

After a prolonged dispute between the Foreign Ministry and the chancellor's office over the nature of an SDI accord with Washington, the Kohl government now seems prepared to approve terms of participation for West German companies eager to win lucrative contracts under the $26 billion missile defense program. A Bonn spokesman announced today that a final Cabinet decision is likely by the end of the month that will lead to an exchange of letters between Bonn and Washington.

West German officials said the way was cleared for an agreement when Defense Secretary Caspar W. Weinberger and his British counterpart Michael Heseltine approved a framework accord that will make Britain the first allied participant in the antimissile research project.

Foreign Minister Hans-Dietrich Genscher has insisted that the Bonn government must not be isolated from its European partners in joining the Strategic Defense Initiative because of the risk that Moscow would single out West Germany as a target for renewed political pressure, perhaps through threats to its relations with neighboring eastern countries.

Zagladin's remarks today seemed to vindicate Genscher's fears. The Soviet official bluntly charged that the Kohl government's plans to participate in the space antimissile defense project would shatter credibility in Bonn's frequent exhortations to the superpowers to respect arms control pacts and to work toward improved East-West dialogue.

"There is a contradiction in the [Bonn] government's position," Zagladin said. "On the one hand, it endorses existing treaties but on the other it proposes an exchange of letters which would undermine the ABM treaty."

According to Article 9 of the 1972 ABM pact, the United States and the Soviet Union agreed "not to transfer to other states, and not to deploy outside its national territory, ABM systems or components" restricted by the treaty.

A further elaboration was made in "Agreed Statement G," which stipulated that the United States and Soviet Union would not provide to other states "technical descriptions or blueprints specially worked out for the construction of ABM systems and their components."

Apparently seizing on the phrase "technical descriptions or blueprints," the Soviets appear to be pressing West Germany to recognize that any research findings or information gleaned from SDI work could be fairly perceived as a violation of the ABM treaty.

The Kohl government and other European allies were instrumental recently in persuading President Reagan to reaffirm a strict interpretation of the ABM treaty provisions, despite attempts by the Pentagon to adopt a broader view to remove constraints on SDI testing.

Genscher has called the ABM treaty the "Magna Carta" of the Bonn government's arms control policy and Kohl has vowed that any West German involvement will be scrupulously governed by adherence to the treaty.

Zagladin also questioned the sincerity of Kohl's support for closer East-West dialogue by contending that Bonn's favorable attitude toward participation in the Stratetic Defense Initiative worked at cross-purposes with declared wishes for a positive outcome at the Geneva summit.

"The chancellor says he wants success at Geneva but what he is actually doing is ruining the chances of achieving that success," Zagladin said. The Soviet Union, he added, wanted "to achieve as much as possible at the summit, and certainly make real steps in the direction of arms control."

"We are no great optimists because we know the position of the United States. But we are also no great pessimists because we know that peaceful coexistence is necessary to all," Zagladin said.