The Washington Post reported incorrectly in yesterday's editions that the Soviet Union is producing the "Backfire" bomber at a rate of 30 a month. The correct rate is 30 year.

In December 1974, on a plane carrying President Ford And his party to Tokyo from the Vladivostok summit, Henry A. Kissinger gave one of his famous background briefings to reporters.

The subject was the new strategic arms limitation treaty (SALT), tentatively achieved at Vladivostok, and Kissinger was asked if the Soviets' Backfire bomber would be covered by the new accord.

No, Kissinger replied, Backfire had not been mentioned at Vladivostok, so it would not be covered by the overall limits agreed to there on the two superpowers' strategic weapons.

In effect, Kissinger said Backfire was a medium-range, not a long-range strategic bomber.

Almost immediately Kissinger decided this was too definitive a statement. Copies of the transcript of that background briefing were withdrawn, and the State Department said they would be unavailable.

As it turned out, that Kissinger backgrounder baptized the Backfire as a new SALT issue. Previously, the swing-wing, supersonic bomber had provoked heated debate inside the U.S. government and some public comment, but only after Vladivostok did the plane become a point of serious ppublic controversy.

When the formal SALT II debate begins Monday in the Senate Foreign Relations Committee, Backfire is likely to be one of three substantive issues that gets the most attention. (The other two are verification and the Soviets' 308 "heavy" supermissiles.)

Numerous critics of SALT II and some uncommitted senators have asked publicly how a bomber that everyone agrees could be used against the United States could have been excluded from the numerical limits of the new treaty.

The answer to that question amounts to an encapsulated account of the delicate combination of winks and compromises that produced the SALT II agreement. The Carter administration is confident that it can satisfy senators that the Backfire can safely fe left outside of SALT, but some of the treaty's opponents are confident that the Backfire will be a potent argument for amending or rejecting the past.

The first Backfire (the designation is NARO's) was flight-tested in 1969.

A modified version appeared soon after, and went into production. In 1974 the plane came into service.It is used by both the Soviet Air Force and the Soviet Navy.

From the beginning Backfire has divided American intelligence analysts. In the mid-1970s, according to a senior government official at the time, the Defense Intelligence Agency and the CIA produced widely differing estimates of the Backfire's range, so different that the White House had to order the two to produce a figure or figures on which they could agree.

To this day U.S. intelligence on the Backfire - the Soviets call it a TU22M - is not as good as officials would like. According to informed sources, the United States knows a good deal more about the Soviets' principal missile systems than it does about Backfire.

On one point there is no debate: at present, the Backfire is deployed as a "theater" weapon, for potential use in Europe and China, and as a sea-patrol aircraft. Nothing in its history so far, the way the plane is based, the training missions it flies, and so on, suggests that the Soviets envision using it against the United States.

But airplanes are flexible weapons, and theoretically at least, the Soviets would have little difficulty altering the Blackfire's mission.

When used for short-hand medium-range missions, the Backfire can fly supersonically and at low altitudes. But flying that way consumes fuel rapidly. To reach the continental United States, the plane would have to fly at a high altitude and a relatively slow speed. On the other hand, if a Backfire were refueled in flight, a theoretical possibility, it could fly lower and faster on a mission to the United States.

The Backfire is clearly a lesser plane than the bombers that are counted under SALT, but nevertheless it shares an ability to strike the United States.This is the essence of the Backfire ambiguity.

However, it is not the only ambiguous weapon in this picture. The U.S. F111 and FB111 swing-wing planes also raise questions. Sixty-six FB111s armed with thermonuclear bombs and based in Portsmouth, N.H., and Plattsburgh, N.Y., are part of the Strategic Air Command force targeted against the Soviet Union.With one in-flight refueling, these planes can strikes targets throughout European Russia, and that is their principal mission today.

These FB111s are not counted under the SALT treaty's limits.

In addition, the United States maintains about 350 F111s, slightly less capable planes, 160 of which are based in Britian, and targeted against the U.S.S.R. The other F111s based in the United States could be moved to Britian to join those 160 in a crisis. Flying from British bases, the F111s can hit targets over most of the Soviet Union.

The F111s also are not counted under SALT II.

The Soviets now have 150 Backfires, and are producing them at a rate of 30 a month. At the Vienna summit Soviet President Leonid I. Brezhnev assured President Carter that this rate would ramain constant.

In a formal note, the Soviets pledged not to "increase the radius of action of this airplane in such a way as to enbale it to strike targets on the territory of the U.S.A." This phraseology is ambiguous, since the term "radius of action" suggests round-trip missions, and even U.S. bombers aren't programmed to return home from an attack on the U.S.S.R.

At Vienna also the United States said it would regard any Soviet effort to improve the Backfire's capabilities as inconsistent with the assurances the Soviets gave. But the Soviets said they would not be bound by any such unilateral American statement. The two sides agreed to disagree on that point.

During the SALT II negotiations, the two superpowers did not arrive at an agreed definition of a "heavy bomber," though they did agree that such bombers should be counted under the overall limitations.

In practice this means that Soviet Bison and Bear bombers, both 1950s' vintage, and U.S. B52s and B1s are counted. The Backfire is smaller than all four of these. The FB111 is smaller still.

There has been a series of American gambits during the negotiations to somehow count or account for the Backfire in SALT. The Soviets have agreed to talk about the matter, but only once showed any willingness to incorporate a limit on Backfire into a SALT pact.

That one instance was in early 1976, according to Gerald R. Ford's recently published memoirs. The Soviets showed interest in a proposal advanced by Kissinger that would have limited the Soviets to 275 Backfires by 1981, and would also have put restrictions on the plane's "Deployment and operations."

In return, the United States offered to abandon submarine-based, long-range cruise missiles, a type of weapon not yet in use.

That Kissinger proposal foundered when Ford decided he could not afford to make a SALT agreement during the 1976 primaries, when Ronald Reagan was peppering him from the right wing. But the limits on Backfire it included were modest in any event.

Since early 1975 American officials have seen Backfire as a bargaining chip that could be used to protect American cruise missiles, the newest type of strategic weapon and one the Soviets have not yet matched. SALT II does permit the United States to proceed with deployment of air-launched cruise missiles and development of other types, and administration officials sometimes argue that leaving Backfire uncounted helped make this possible.

Carter administration officials also argue that leaving Backfire out of the SALT II limitations was the price the United States had to pay to leav out American "forward-based systems" and the French and british nuclear forces. The forward-based systems, bombers stationed in Europe and on U.S. carriers, give the United States thousands of nuclear bombs that can be used against Soviet targets but aren't counted in SALT.

The Joint Chiefs of Staff and some other elements inside the American bureaucracy have argued repeatedly that, it Backfire has the capability to attack the United States, it should be counted in SALT.

But more than once the JCS has approved SALT proposals that left the plane uncounted, in return for other provisions they thought would balance Backfire.

The JCS signed off on the Carter administration's March 1977 "comprehensive" SALT proposal, later rejected by the Soviets, and they have signed off on the new SALT II treaty, both of which excluded Backfire.

Some critics of SALT II argue that the Backfire issue has symbolic importance beyond its substance. They contend that excluding the Backfire from SALT limits amounts to a one-sided concession to the Soviet Union in a treaty that is supposed to provide equality.

Defenders of the Backfire arrangement respond that the treaty also permits the United States to do things the Soviets can't match.

And beyond that, the practical aspects of Backfire cannot be ignored. Specifically, they argue, a Backfire attack against the United States would take 10 hours from takeoff to bombs-away, a fact that makes the bomber irrelevant to the initial phase of a nuclear war.