If the Soviet Union equips its Backfire bombers with long-range cruise missiles, that would make the controversy over the plane "easier to deal with politically," the Department of State said yesterday.

The statement by department spokesman Hodding Carter III was the only public reaction by the Carter administration to the disclosure that the Soviets have conducted several tests of long-range, airlaunched cruise missiles, and that intelligence experts believe the Backfire was the launch platform.

Privately, however, administration sources said that the surprise tests appear to pose no special problem because a Backfire bomber armed with cruise missiles with a range of more than 600 kilometers -- 373 miles -- would be classified as a strategic weapon against the ceiling set in the strategic arms limitation treaty (SALT) now being negotiated.

As SALT II now stands, Backfire is not counted as a strategic launch vehicle. Backfire is the North Atlantic Treaty Organization's designation for the Soviet bomber.

Sources said that it was no surprise that the Soviets had begun flight-testing long-range, air-launched cruise missiles because they have pursued cruise missile technology for years. But U.S. officials said that they lag substantially behind America in guidance techniques and in reduction of missile size.

What was surprising was that the first test of a long-range, air-launched cruise missile apparently employed the Backfire bomber, a plane that has been controversial because skeptics of SALT II insist it has the capability to attack the United States, making it a strategic rather than a theater weapon.

One congressional source said that for the Soviets to use such a plane in the test of the new long-range missile "makes no sense whatever."

The source said that it is "highly unlikely" the Soviets would employ the Backfire only to test-launch a new missile. If the Backfire is being used in tests, he said, it is probable that the Soviets intend to deplly operational Backfires with the missile.

Cruise missiles, unlike ballistic missiles, are lowflying, relatively low-speed unmanned winged vehicles designed to reach their targets by flying beneath radar coverage and taking advantage of terrain.

The United States has cast its lot heavily with long-range cruise missiles for modernizing its B52 bomber force.

Under terms of SALT II being negotiated at Geneva, the United States and the Soviet Union each will be permitted to have 2,250 strategic launch vehicles, with 1,320 of them permitted to carry multiple warheads.

If Russia began to deploy the Backfire armed with long-range cruise missiles, it would be required under the treaty to dismantle one ballistic missile launcher for each plane. The Backfire, armed with long-range missiles, would count not only against the total ceiling, but also against the limit of 1,320 launchers with multiple warheads.

The test missiles fired from the air in recent weeks are reported to have flown about twice as far as the Soviet cruise missiles tested earlier -- some 1,200 kilometers, or 750 miles -- and some sources believe the range may be extended substantially beyond that.

In its development of long-range cruise missiles, which it plans to deploy on its B52 bombers, the United States made considerable use of the A6 tactical attack aircraft as a launch platform.