In each of the past five years, the Soviet Union has built 32 or 33 Backfire bombers despite a U.S. claim that then-Soviet President Leonid I. Brezhnev pledged in 1979 not to increase the production rate above 30 a year, according to sources who have studied U.S. intelligence agency reports.

Because the Brezhnev pledge was made as a side agreement to the SALT II strategic arms limitation treaty, a White House interagency working group has agreed tentatively to include the Backfire bomber in a list of new Soviet violations of arms control agreements, according to sources.

But a detailed review of the Backfire issue shows not only a disagreement between the U.S. and Soviet governments on the production number but also illustrates that arms control compliance mirrors internal bureaucratic battles in both governments and their intelligence agencies.

One recent U.S. intelligence report said the Soviet Backfire production rate in 1978 and 1979, the years before the SALT II statement, was 31 bombers a year, according to sources. But at the June 1979 Vienna summit and thereafter, the U.S. position was that "President Brezhnev confirmed that Soviet Backfire production rate would not exceed 30 per year," according to the official State Department text on the "Soviet Backfire statement."

That same intelligence report showed production at 32 Backfires a year in 1980, 1982 and 1983, and at 33 a year in 1981 and 1984, sources said.

When the Backfire production rate was brought up to the Soviets in Geneva recently, according to informed sources, the Soviets said that they are following Brezhnev's promise not to increase production "as compared to the present rate." But the Soviets disputed the United States' 30-a-year figure, these sources said.

Specialists on Soviet arms, both in and out of the administration, said U.S. intelligence shows conclusively that Moscow is consciously breaching the Backfire limit of building 30 a year, and are even building at the 31-a-year rate. But there is no agreement on why Moscow is doing it.

The additional bombers do not give the Soviets any serious military advantage, sources said. But the extra production illustrates what one former high Defense Department official called a tendency to "thumb their noses at limitations they don't think necessary."

This official pointed out that Soviet military men did not want to include the Backfire, which they consider a medium-range bomber, in the SALT II agreement and were unhappy when Brezhnev agreed to the side deal under pressure from President Jimmy Carter.

Other officials said the Soviets intentionally undercut agreements, such as that dealing with the Backfire, to test U.S. intelligence capabilities to discover them, or to see if the U.S. political will is strong enough to respond, or because Soviet bureaucrats are indifferent to agreement language.

Moscow's attitude toward arms control compliance has been made a major issue by the Reagan administration, which sent Congress a report on seven violations last January and plans another next February.

At the same time, administration officials stress that verification provisions, including cooperative and on-site measures, will have to be included in future arms control agreements because of the pattern of Soviet violations.

"The chiseling on the Backfires goes on intentionally," said Steven Meyer of the Massachusetts Institute of Technology. He added that U.S. ability to discover it and other alleged violations shows that verification arrangements have worked.

Meyer said he also believes the Soviets have "deliberately exceeded" the 150-kiloton limit on the 1974 underground nuclear testing treaty, also cited in the January White House report. That agreement, as with SALT II, has not been ratified by the United States but both superpowers have declared they would abide by its provisions.

One purpose that Meyer and others see in such activity is to keep a check on U.S. intelligence. The classic case involves continued U.S. complaints that the Soviets are encrypting -- making impossible for American electronic intelligence collectors to understand -- the radio messages on performance data sent from their test missiles as they travel through space to their targets.

Under SALT II, in another understanding that the Soviet military opposed, Brezhnev agreed that neither nation was to interfere with the other's collection of information on these missile tests.

When the United States complained at the special Geneva commission set up to handle such arms control problems, the Soviets have asked what information the U.S. government are unable to collect.

Rather than give away interception capabilities, U.S. officials have been pressing the Soviets to stop encoding all their telemetry data.

One former top Defense Department official, who has dealt directly with top Soviet officials, said, "They like to put something over on us. . . . It gives them a 'victory.' "

This official said he believes the Soviet decision to locate a phased-array radar in central Siberia probably violates the 1972 SALT I treaty, but that it was placed there because "somebody decided it was too expensive to put it where the treaty requires."