The Senate Foreign Relations Committee yesterday heard suggestions that it should approve the new SALT pact but add to it a resolution calling for immediate and significant reductions in the nuclear arsenals of the two superpowers.

Yesterday's hearings on SALT II provided the first occasion for the public discussion of this idea, one that a number of senators and some administration officials have been considering privately.

One version of it was offered by Sen. George McGovern (D-S.D.). McGovern said he would soon introduce "arms reduction" legislation to be tacked on to the Senate's resolution of ratification of SALT II.

This legislation would instruct American negotiators to begin at once to seek an immediate freeze for a year on deployment or development of any new strategic weapons, then initiate a program of 10 percent annual reductions in strategic forces and seek a summit meeting after three years to reevaluate that percentage.

"I cannot support SALT II as presently constituted without some such accompanying resolution based on what I believe is the emerging consensus of both 'hard-liner' and longtime advocates of arms limitation," McGovern said. By itself, he added, the new treaty will provide for much bigger Soviet and American arsenals even as senators of all persuasions declare they are for reductions instead.

Later in yesterday's hearings, Jeremy J. Stone, executive director of the Federation of American Scientists, expanded on a similar idea, warning the committee that "the SALT process will self-destruct by 1985" if successive agreements provide only new rules for continuing escalation of the arms race.

Doves and hawks would both likely conclude that SALT is meaningless unless it begins to control armaments, Stone said, arguing for a plan of steady precentage reductions in all categories of both countries' arsenals.

"There have to be very specific assurances demanded by the Senate" for a better treaty next time, Stone said.

He said SALT I "missed the boat" by limiting only missile launchers at a time when individual warheads were about to proliferate, and that SALT II misses the boat by limiting warheads when warhead accuracy is improving dangerously. He predicted the new generation of cruise missiles - unmanned drones with uncanncy accuracy - will bedevil SALT III.

Yesterday morning three former chief SALT negotiators testified to the committee. U. Alexis Johnson, who led the negotiators in the second Nixon and Ford administrations; Gerard C. Smith, who negotiated in the first Nixon administration, and Paul C. Warnke, from the current administration, all supported SALT II.

Last week the man who worked under Johnson and Warnke as the Joint Chiefs of Staff representative on the SALT delegation, Lt. Gen. Edward J. Rowny, accused the United States of not knowing how to conduct negotiations with the Soviets and of making a steady string of concessions, getting nothing from the Soviets in return.

Only a few senator's questions to the former SALT negotiators yesterday picked up on Rowny's accusations. All of them were greeted with sharp denials. Johnson also challenged the accuracy of Rowny's description of important events in the negotiating.

Warnke said that SALT II put no serious limitations on the United States, but substantially restricts Soviet strategic programs. He said he sympathized with complaints that the treaty did not do enough, but added that one cannot expect to get a great deal in a negotiation if one is not prepared to give things up in return.

At one point Warnke indicated that he had favored more American concessions to get more limits on Soviet forces, but that he had been overruled in interagency debates in Washington.

Sen. Jesse Helms (R-N.C.) deplored SALT II as a treaty that would only escalate the arms race. He told Warnke: "I don't see why this nation doesn't go back to the drawing board and put on an international public relations campaign on behalf of arms reductions." CAPTION: Picture, Former SALT negotiators Paul C. Warnke, Gerard C. Smith and U. Alexis Johnson, from left, testify before panel. AP