The chief of the Soviet general staff opened up the possibility of a major Soviet expansion in space-based defensive weaponry and said that "there will be no American monopoly in outer space."

Marshal Sergei Akhromeyev threatened that if the Reagan administration's Strategic Defense Initiative is continued, "nothing will remain for us but to adopt countermeasures in the field of both offensive and other armaments, not excluding defensive ones, and including those based in outer space."

He said that the Soviet Union "cannot show naivete and count only on peaceful assurances by U.S. leaders that serve as a cover for developing strike weapons in space."

Akhromeyev's comments, in an article in Saturday's edition of the Communist Party newspaper Pravda and distributed tonight by the official Tass news agency, appeared to expand the scope of the threatened Soviet response in the field of space weaponry.

He also accused the Reagan administration of "falsifying and publicly discrediting" Soviet arms control proposals and distorting with "deliberate deceit" their interpretation of the 1972 Antiballistic Missile Treaty in order to pursue plans for the space-based Strategic Defense Initiative, or "Star Wars" antimissile system.

Akhromeyev said the treaty "unambiguously bans" development, testing and deployment of space- and land-based ABM systems.

He rejected arguments that the treaty does not apply to testing and development of lasers, beam weapons and other "exotic" ABM programs. It strictly limits research and testing of ABM systems and their components, based on other physical principles, he said. Neither side can deploy systems in these "limited areas," he added, without preliminary consultations with the other side, and without introducing amendments in the treaty.

According to current U.S. administration policy, the ABM treaty permits testing and development of antiballistic missiles using "other physical principles" such as lasers and directed energy weapons, a White House official said in Washington last week.

The Soviet defense official clarified the Soviet stand on research on space-strike weapons, saying Moscow considers "impermissible . . . any type of out-of-laboratory work connected with development and testing of models, pilot samples, separate assemblies and components."

He continued: "Everything that is being done for subsequent design and testing of space-strike weapons should be banned."

But he said that the Soviet position "does not deny the right and possibility to conduct basic research in outer space."

Akhromeyev's description is the most detailed public explanation of the Soviet position on space-strike weapons since Soviet leader Mikhail Gorbachev outlined the Soviet opposition to out-of-laboratory SDI research in an interview in Time magazine in August.

Western analysts here interpret Akhromeyev's strict definition of the testing allowed by the ABM treaty as a signal to Washington of the limits of the Soviet position on SDI research, widely viewed here as one of the key issues on the agenda for the summit meeting between President Reagan and Gorbachev in Geneva in November.

In the sharpest criticism of the U.S. approach to the summit meeting since Soviet Foreign Minister Eduard Shevardnadze met with senior U.S. officials last month, Akhromeyev said that Washington has shown "no signs of businesslike and constructive preparations for the meeting."

"The Soviet position is being distorted," he said, adding that "real facts are being presented in a crooked mirror, and attempts are being made to spread in the world doubts about the sincerity of the Soviet Union's positions."

But a U.S. official in Moscow, following a summit preparatory meeting between U.S. Ambassador Arthur Hartman and Shevardnadze, described the "hopes" of both sides for the meeting as "realistic." He said, "Their hopes are as realistic as ours. They don't see this as a breakthrough meeting."

Senior western diplomatic sources in Moscow said it was unlikely that an arms control agreement would be reached during the meeting, but that there is "a good chance" that an exchange agreement encompassing Soviet-American academic, cultural and exhibit exchanges will be ready to be signed at that time.

A U.S. official based here said the Soviet arms control proposals outlined early this month in Paris by Gorbachev prepared the way for "a serious discussion."

But Akhromeyev batted back some of the western criticisms of the Soviet proposals.

In apparent response to Reagan's charge last Saturday that Moscow is developing its own Star Wars program, Akhromeyev said, "The Soviet Union is not engaged in developing and consequently testing any models of space systems whatsoever. We do not have a program of creating space-strike systems or Star Wars plans analogous to the American ones."