The Pentagon is studying "possible options" that include going beyond present arms control treaties on offensive nuclear weapons and hastening development of "missile defenses of our own" if the Soviets break away from the 1972 Anti-Ballistic Missile Treaty, Assistant Secretary of Defense Richard N. Perle said yesterday.

His testimony before the Senate Armed Services Committee went further than any administration official has before in suggesting how the government might respond to a Soviet "breakout" from the terms of the ABM pact, which limits both powers to one major ABM site.

The administration says there are signs that the Soviets may be moving instead toward a nationwide defensive system.

That is one of a number of arms treaty violations U.S. officials have charged to the Soviets in recent months. Officials now have begun to use these reported violations in Congress to justify the president's defense budget and his proposed Strategic Defense Initiative -- his "Star Wars" research plan to develop a futuristic missile defense system in space.

Perle cited a long string of what he called "militarily significant" Soviet arms violations, then told the committee, "We must now create penalties for violations that deny the benefits of the violations to the U.S.S.R. . . . This could involve research, development or deployments which at least offset the advantage obtained by the Soviets."

He warned that such actions would be expensive, but added that unless Congress appears ready to endorse retaliatory steps, "we would simply encourage the Soviet Union to further erode the ABM treaty."

Kenneth L. Adelman, director of the Arms Control and Disarmament Agency, announced to the same panel "the apparent cessation of chemical weapons use in 1983 and 1984, if our information is correct, by the Soviets and their surrogates in Afghanistan, Laos and Cambodia."

Adelman said he hopes "it was forthright exposure of the violations by the United States . . . which influenced Soviet behavior."

The Thai government on Tuesday accused Vietnam, one of Moscow's allies, of using toxic chemicals against Cambodian rebels. But a spokesman for Adelman said last night that the administration has no independent confirmation of the report.

The State Department's director of politico-military affairs, Lt. Gen. John T. Chain Jr., also appeared at the closed-door session. Unclassified versions of their prepared statements were released to reporters while the three officials still were testifying.

Perle said that the Soviet treaty violations, detailed in a report sent to Congress Feb. 1 by President Reagan, would be "a significant element of new arms-control negotiations with the U.S.S.R."

Reagan said in his Feb. 1 report that the Soviet Union "had violated the ABM treaty" by locating a large phased-array radar facility in central Siberia near Krasnoyarsk. A phased-array radar, a form of three-dimensional radar, cannot be located so far inland under the ABM treaty.

Chain said, "It will . . . be difficult to move ahead in the defense and space forum at the Geneva negotiations without a satisfactory resolution of the Krasnoyarsk issue." Adelman said the Geneva negotiations "can give us another channel for trying to get the Soviets to abide by existing agreements."

Perle stressed that Soviet violations of the ABM and SALT II agreements and the treaty banning use of chemical weapons "are militarily significant" and thus required some U.S. military response.

He said the Soviets "have amassed, for example, a major advantage in chemical weapons;" they "will have a new MX-sized rail mobile missile capable of refire in a relatively short period of time . . . and are also moving toward deployment of a new small, mobile ICBM which will be capable of refire."

Perle detailed no possible penalties for Soviet violations. "It need not be a tit-for-tat," he said. "It may not suit our purposes to build a Krasnoyarsk radar in Wyoming."

One discordant note between the sometimes feuding State and Defense officials popped up over the Standing Consultative Commission, the Geneva-based group set up under terms of the 1972 SALT I treaty to serve as a forum for Washington and Moscow to discuss differences over compliance.

Chain called the confidential discussions of the commission "an important part of our compliance policy." Perle, however, said it "has been largely unsuccessful over the years in resolving serious compliance concerns" and, "unfortunately, previous administrations have exaggerated its effectiveness in order to sell unverifiable arms-control agreements to the U.S. Congress."

Perle said the commission is "only a forum for meetings" out of which "nothing constructive can emerge if one side refuses to acquit itself in a constructive manner."

The State Department, meanwhile, dismissed Soviet Foreign Minister Andrei A. Gromyko's latest objections to the U.S. "Star Wars" program as a "familiar Soviet position."

Gromyko warned that the U.S. plan for outer space "dramatically heightens the threat of nuclear war." He said negotiating reductions of offensive missiles would be "out of the question" while the United States realizes "its designs with respect to space.