U.S. policy toward the Soviet Union should remain on the present course in the face of a dramatic strengthening of the domestic position of Soviet leader Mikhail Gorbachev, the State Department's senior Kremlinologist testified yesterday.

Deputy Assistant Secretary of State Thomas W. Simons Jr. told the Joint Economic Committee of Congress it is far too early to tell whether Gorbachev's rule will produce "a freer and more benign" Soviet Union in the U.S. interest or "an economically more robust U.S.S.R. {which is} a more formidable foe."

In the meantime, Americans must be "realists" who respond to concrete Soviet acts rather than rhetoric, Simons said, and at the same time "avoid sending signals to the Soviet leadership which could inhibit positive change without advancing U.S. interests."

Simons, the department's ranking career expert on Soviet affairs, described Gorbachev's domestic policies as an improvised set of reform measures that began modestly and have gone "from piece to piece" as the Soviet leadership has proceeded along "a learning curve."

By late last year, Simons said, the prospects for Gorbachev's effectiveness as Soviet leader and for serious reforms seemed to bog down, and early this year his plans seemed stymied at the January plenum of the Soviet Communist Party.

But this June's Communist Party plenum "confirmed a dramatic shift" in Gorbachev's favor, including official approval of his ambitious economic programs and the addition of three close associates to the ruling Politburo. "Gorbachev emerged with a stronger political position" and has obtained "an extensive mandate for change," Simons said.

Whether the Soviet leader will be able to make good on that mandate and successfully direct a fundamental restructuring, however, is a question that will take many years to answer, Simons added.

"Neither our hopes nor our apprehensions are likely to be fulfilled over the next three years. Gorbachev's short-term economic policy objectives will be difficult to achieve, and the results are almost certain to be inconclusive," Simons said.

In this period, he said, "The basis characteristics of the relations between the United States and the U.S.S.R. will continue to pertain. The Soviet Union will remain the powerful adversary we have successfully contained for over two generations."

Simons' testimony and that of three Soviet experts from private life came one day after a bipartisan study group sponsored by the Institute for East-West Security Studies called for the United States "to respond creatively to the opportunities offered by the new direction in Soviet policy."

Simons praised the new study as "a quite sound document . . . consistent with the approach we already have."

However, Prof. Jerry F. Hough of Duke University, one of the private Sovietologists who testified yesterday, described Simons' testimony as "rather disappointing" and called the State Department approach "profoundly wishful thinking . . . that we don't have to worry, we can just stay the course."

Unless the United States responds more creatively to the changes in Moscow, Hough declared, Gorbachev "will continue to blow us out of the water as he has for the last few years."

Hough described Gorbachev's domestic political position as "enormously strong," comparable to that of Josef Stalin in 1928-29. In intention Hough compared Gorbachev to Peter the Great, czar from 1682 to 1725, and said the current leader is seeking to reopen Russia to the West, especially in the economic sphere.