The Carter administration will press anew in Moscow next week for a side agreement designed to keep the Soviet Backfire bomber from posing a prime threat to the United States.

The idea, according to administration officials trying to wrap up a strategic arms limitation talks (SALT) agreement with the Soviet Union, is to induce the Soviets to pledge separately that they will limit the production and missions of Backfire.

With a limited number of Backfires confined to patrolling sea lanes in an anti-ship role and to training for a theater rather than for all-out nuclear war, these officials argued, the bombers would represent a small enough risk to be covered outside the formal SALT agreements.

The United States could keep track of how the Soviet Union was training its crews to fly Backfire, these officials added, and could detect in a hurry whether the distinctive flight patterns for nuclear bombing were being practices.

U.S. intelligence officials concluded, that Israel had nuclear boms after determing that some of the flight profiles its pilots were practicing would only be used for nuclear strikes.

At the moment, the Soviets are committing every other Backfire coming off the production line to the role of patrolling Atlantic and Pacific sea lanes from staging bases in northern and eastern Russia.

U.S. Navy leaders regard Backfire equipped with air-to-surface missiles as a prime threat to carriers and other ships.

If a side agreement limited the total number of Backfires the Soviet Union could produce and half that number remained committed to the anti-ship mission defense officials involved with the SALT negotiations contended that the threat to the United States from Backfire would be diminished.

U.S. critics of President Carter's draft SALT proposals have argued that the Backfire could drop nuclear bombs on the United States and thus should be counted as a strategic weapon in any new arms control pact.

A written Soviet pledge to confine Backfire to non-strategic missions could be broken overnight, these critics contend.

The Joint Chiefs of Staff, whose endorsement could be pivotal in getting any SALT agreement through the Senate, have gone on record in favor of counting Backfire as a strategic, heavy bomber.

Air Force Gen. George S. Brown, outgoing chairman of the joint chiefs, said in his posture statement sent to Congress in January:

"The Joint Chiefs of Staff have recommended counting the Soviet Backfire in the aggregate since it has characteristics and capabilities similar or superior to those aircraft which both sides agree are heavy mombers.

"While estimates of maximum range differ, the Backfire can deliver ordinance on the United States and recover in third countries without refueling. In wartime the Soviets could employ the Backfire against the United States . . . Over 100 Backfires have probably been produced."

The Backfire has a swing wing like the U.S. Air Force's FB111 bomber, which is not counted as a heavy bomber under the current SALT agreement.

If a SALT II agreement cannot be negotiated for failure to resolve such disputes as the one over Backfire, U.S. spending on strategic weaponry is expected to rise sharply. Defense Secretary Harold Brown estimates that an additional $2 billion a year would have to go into long range missiles and bombers if there is no SALT agreement.

Another hazard of failing to reach an agreement, in the view of Pentagon officials pushing for one, is the collapse of the whole SALT process. This collapse, in turn, would chill political relations between the two superpowers, they predict.

The Backfire and other arms control issues will be discussed when Secretary of State Cyrus R. Vance arrives in Moscow on Wednesday for three days of talks with Soviet leaders.