The Reagan administration will not resume negotiations to halt nuclear weapons testing until the superpowers have made deep reductions in their current nuclear stockpiles, according to Pentagon and other officials.

This hardening of the U.S. position has come at a time when there have been advances in techniques to verify underground nuclear explosions, and Soviet leader Mikhail Gorbachev has embarked on a major worldwide campaign to bring about a comprehensive test ban.

Atmospheric nuclear tests were banned by the superpowers in a 1963 treaty but underground tests have continued. In 1974, Moscow and Washington agreed to limit underground tests to less than 150 kilotons, although the accord has never been ratified by either side. The United States has resisted Gorbachev's proposed comprehensive ban on grounds that testing is necessary to keep a reliable stockpile, build a new generation of nuclear weapons and that a ban would be difficult to verify because of difficulty in detecting small detonations.

Speaking for the administration, Assistant Secretary of Defense Richard N. Perle recently told the Senate Foreign Relations Committee, "I don't believe in a comprehensive test ban in a period when the United States is depending on safe, reliable nuclear weapons."

An even tougher line was taken by the Arms Control and Disarmament Agency (ACDA), which in submissions to the House Foreign Affairs Committee said that before the United States resumes negotiations on a comprehensive ban, there must be an agreement on "deep reduction in the levels of nuclear weapons, maintenance of a credible nuclear deterrent, improved verification capabilities and expanded confidence-building measures."

In one document, the ACDA said that "the U.S.S.R.'s superiority in conventional forces must be dealt with before we abandon our nuclear deterrent" and thus nuclear testing. In another document, the ACDA wrote that negotiations for a comprehensive ban should not take place even if verification problems associated with such an agreement were completely solved.

Nonetheless, the ACDA said that a ban agreement remains a "long-term goal of U.S. policy." As Perle put it, administration interest in a test ban would revive when "we reach that time where the role of nuclear weapons has declined."

At a House Armed Services Committee panel on arms control yesterday, Dr. Lynn R. Sykes, a Columbia University professor and Pentagon consultant, said that "recent advances in seismology ensure that attempts to detonate clandestine explosions" under a test ban "will be even easier to detect than was thought only a few years ago."

He said that new seismic technology in Norway capable of detecting high-frequency signals has recorded an explosion "of about one-half kiloton" at the Soviets' central test site 2,600 miles away.

The "main impediments" to the Reagan administration seeking any new testing agreement "are neither scientific nor technical but rest on the notion that the security of the United States is best enhanced by continued testing and development of new atomic weapons," Sykes added.

The United States, which in the 1970s detonated about 12 underground tests a year at its Nevada test site, increased that number to roughly 16 a year under the Reagan administration, according to a chart Sykes presented to the committee.

Such tests are used in part to determine the feasibility of an X-ray laser, beams created by a nuclear explosion that could be used in the president's Strategic Defense Initiative (SDI), the "Star Wars" research into a shield against nuclear missiles.

The Soviets, who increased their tests in the 1970s from 15 to as many as 30 in one year, have cut back to 10 a year since 1980, according to Sykes. In August, Gorbachev announced a test moratorium until January while promising to extend it if the United States followed suit. In a Nov. 7 message to six world leaders who volunteered to monitor a test ban treaty, Gorbachev said that a halt in testing would "preclude practical work to upgrade qualitatively nuclear weapons, develop new types and enhance their destructive . . . effect."

For reasons that remain unclear, administration officials told Congress they believe a testing halt would erode confidence in stockpiled U.S. nuclear weapons more than it would the Soviet force.

For example, Donald Kerr, director of the Los Alamos Scientific Laboratory, told the House Foreign Affairs panel that it was "quite possible" that Soviet weapons would be less affected over time than those of the United States.

Sykes, however, said that with continued testing the Soviets would be able to create "lighter-weight weapons on their large intercontinental missiles." And since their missiles were larger than those of the United States, lighter warheads would allow them to put more bombs on each missile.