The Reagan administration's top salesman for the Strategic Defense Initiative told Congress yesterday that a "compelling case" could be made within five years for the controversial project on the basis of "convincing laboratory tests" without the Pentagon conducting tests in the atmosphere or underground.

Appearing at the first session of the new Defense Policy Panel of the House Armed Services Committee, Lt. Gen. James A. Abrahamson, director of the SDI program, sought to assuage congressional fears that research on the feasibility of the space-based defense system eventually would require testing of at least some parts of it in open violation of the 1972 antiballistic missile (ABM) treaty.

Abrahamson acknowledged that the administration would not be able to present "a perfect case" to Congress while complying with the treaty's ban on the development and testing of antiballistic missile systems or any sea-, mobile land-, space- or air-based components.

He also warned there was a point where pure research reached the level of "development" and would raise potential problems with treaty compliance.

He maintained, however, that knowledge about its workability would be "substantial enough" within five years to present Congress "a compelling case" in its favor within the treaty limitations. But he added that it would be "a complex case. No question about it, particularly regarding the defense of populations."

Abrahamson's efforts to convince the new House panel, formed and headed by Armed Services Committee Chairman Les Aspin (D-Wis.), of continuing U.S. respect for the ABM treaty stood in sharp contrast to testimony given Monday to the House Foreign Affairs Committee by Richard N. Perle, assistant secretary of defense for international security.

Perle said it was "a great mistake" for the United States to continue abiding by arms control agreements in light of alleged Soviet violations of their letter and spirit.

Aspin indicated that his central concern was that U.S. research efforts into the feasibility of the SDI, also known as "Star Wars," would undermine the ABM treaty as well as the current strategic balance before there was any assurance that a new agreement could be reached with the Soviet Union.

"The danger is we destroy the system we have now," he said.

As the new chairman of the Armed Services Committee, Aspin is in a position to play a crucial role in persuading Congress to approve, or cut, the $3.7 billion the administration is seeking for SDI research in the 1986 fiscal year.

Aspin said he thought one essential question was drawing up criteria for deciding whether the proposed space-based defense system would work.

"I have a horrible feeling in some sense it will work, but at what level?" he said.

Abrahamson replied that "clear criteria" exist for determining this. He said these included proving the system was technically feasible and affordable in the sense that it would cost the United States "substantially less" to build the system than it would the Soviets to counter it.

A third criterion, the general said, was assuring continued stability in the "transitional period" when the basis of U.S. deterrence was changing from its offensive capability to a defensive one.

"At each step, it's got to show it will make the world safer," he said.