A top Carter policymaker has devised an arms-control strategy that offers escalating concessions to give the appearance of progress in SALT in order to avert congressional interference.

The secret "SALT strategy paper" drafted by Leslie H. Gelb, director of the State Department's politico-military affairs office, affords a rare peek into unguarded thinking at upper reaches of the Carter administration. Gelb's 15-page memorandum, dated July 26, boils down to these two imperatives: First, agreement with the Soviet Union in the strategic arms limitation talks (SALT) transcends mere military considerations; second, restrictions imposed by Congress must be avoided, whatever the cost.

Specifically, the Gelb strategy would extend the present SALT I treaty, due to expire Oct. 3, "through informal means" rather than "formal extension, with the prospect of critical [congressional] hearings and restrictive amendments." Such an administration effort has long been known. But Gelb makes specific how to pull it off& Show some progress on current SALT II negotiations. The Gelb strategy implies such progress is possible only be severely limiting U.S. cruise-missile deployment.

This proposal generated astonishment and distress within the Carter administration when Gelb's paper was circulated six weeks ago. Nevertheless, the strategy being hammered out at high-level meetings last week was a first cousin of Gelb's (though the Defense Department is demanding major changes). Moreover, friendly congressmen are being privately consulted this week about "informal" extension of SALT I.

The "interim accord" curbing inter-continental missiles was signed in Moscow in 1972 as SALT I. If a new SALT II treaty placing overall limits on strategic weapons is not agreed to before Oct. 3, SALT I will expire. this has generated a mood of deep alarm, as is reflected by Gelb's strategy paper.

"No progress on SALT by October frisks further straining overall East-West relations and, in turn, inhibiting cooperation on other bilateral issues," Gelb wrote. "Notwithstanding efforts to downplay its significance, no progress would magnify the negative international and domestic repercussions of a failure to meet the Oct. 3 deadline."

But Gelb, the former New York Times correspondent who is now a mastermind of President Carter's diplomacy, asserts that even with "some progress by October, it is doubtful that a SALT II agreement could be reached sooner than early 1978." What's more, Gelb makes this unusual admission: "The U.S.S.R. has not accepted the major elements of the U.S. proposal and has not even responded to some."

Therefore, Gelb's solution, reflecting the administration's concern about second-guessing from Capitol Hill: "We should plan to extend the interim agreement [SALT I], preferably through parallel, non-binding declarations, avoiding formal extension that would legally require congressional approval."

But Gelb recongnizes that extending SALT I would be dangerous if there were no significant progress in SALT II. "Informal extension would almost certainly be attacked for failure to obtain congressional approval, while formal extension would provide opponents a platform for criticism of the SALT process itself and the conduct of U.S.-Soviet relations. Most worrisome is the prospect that formal approval of an extension might be tied to congressional criteria for an eventual SALT II treaty."

Thus, on top of major retreats made so far, the Gelb paper suggests still more concessions in hopes of giving the impression of progress:

"We would almost certainly have to back down on counting heavy-bomber variants" - the Soviet Bison and Bear bombers - as part of the overall strategic total. "To induce the Soviets to a lower MIRV [multiple independently targeted reentry vehicles] we could agree not to count the 120 disputed silos at Derzhayna and Pervomaysk against the [MIRV] ceiling."

The more startling concessions come on the cruise missiles, the amazingly accurate drone aircraft that has become a replacement for the junked B-1 bomber. The Gelb strategy would stitch into a new SALT II treaty (lasting eight full years) a 2,500-kilometer limit on air-launched cruise missiles. It would also restrict them to as few as 10 missiles per B-52 bomber and 30 per wide-bodied aircraft.

Beyond this, Gelb calls for "an added element of compromise." He suggests a 600-kilometer ceiling on cruise missiles launched from non-heavy bombers as part of the eight-year treaty - not simply as part of the three-year protocol previously offered. Another compromise might be the statistical inclusion of each wide-bodied plane carrying cruise missiles as one MIRV and each B-52 armed with cruise missiles as three MIRVs.

The Pentagon has protested that the cruise missile is vital now that the B-1 is dead, but there is pessimism about overriding the Gelb strategy. The ultimate decision is up to Jimmy Carter, who may soon clarify what he really thinks about these complicated questions of life or death.