The munitions lobby -- including the powerful National Rifle Association -- has teamed up with some friends on Capitol Hill to water down a congressional report on terrorist bombings.

The still-secret study claims that many experts on terrorism "believe that the United States may experience an increase in . . . catastrophic bombing in the years ahead."

Prepared by Congress' Office of Technology Assessment (OTA), the 500-page report explains this alarming consensus as "based upon an assessment of United States vulnerability to bombings and the observation that the United States has recently had less of a terrorist problem than other developed countries."

Aircraft exploding in flight as a result of bombs planted by terrorists, criminals, lunatics, vandals or "experimenters" is the greatest danger, the report states.

The analysis gives this breakdown on perpetrators of bombings, from a study of traceable incidents: The mentally disturbed, 44 percent; vandals and experimenters (whose blasts are usually the least damaging), 40 percent, terrorists, 10 percent, and professionalcriminals, 6 percent.

The exhaustive OTA report was ordered by Sens. Abraham A. Ribicoff (D-Conn.), Jacob K. Javits (R-N.Y.) and others who wanted to assess the possibility of tracing -- or better yet,preventing -- bombings by putting tiny identification particles, or "taggants," in commercially manufactured explosives.

These little i.d. particles, which are detectable by black-light scanners at the scene of an explosion, enable investigators to trace the explosive back to the manufacturer and possibly the retailer, thus narrowing the field of inquiry aimed at the actual bomber. A differrent kind of taggant consists of vapor molecules that permit hidden explosives to be spotted, in much the way airport metal detectors expose guns or "pot dogs" sniff out marijuana.

Although the benefits of a successfulexplosive-tagging program are self-evident, the bill being considered by the Senate Governmental Affairs Committee is opposed by Sen. Ted Stevens (R-Alaska). Stevens is a dedicated handmaiden of the munitions industry, which opposes taggant legislation. He is also a vicechairman of the board that oversees the Office of Technology Assessment. Under pressure from Stevens' office, the original draft of the OTA report was significantly watered down in its appraisal of the bombing danger.

Another opponent with ties to criticsof taggant legislation is Rep. John Dingell (D-Mich.), who like Stevens is a member of the board that has life-and-death power over the OTA. Dingell also is a board member of the National Rifle Association. The NRA opposes tagging, and so does Dingell.

Torn between the facts and pressure from powerful critics, the OTA staff bowed at least partially to the presure.For example, the original draft's warning that the United States "can beexpected to experience" an increase in bombings was reworded to "may experience." And the original reference to taggants as an "extremely useful" tool against terrorist bombings was rewritten, dropping the "extremely" and modifying its usefulness to "most terrorist" bombings.

That last change, sources told my associate Les Whitten, was the direct result of a vehement protest from the NRA's executive director, Neal Knox. At a meeting behind closed doors last Dec. 14, Knox bulldozed the OTA staff into other changes that further diluted the impact of the report.

Even after the barrage by its criticswho complained of the cost and questioned the safety and effectiveness of tagging, the OTA report still contains some compelling arguments for the program.

"Identification taggants would facilitate the investigation of almost all significant criminal bombings in which commercial explosives were used," the report says. And "detection taggants would be very effective in protecting high value targets" such as airports.

Even without the obstruction of the munitions industy and its supporters, it would be 1983 before identification taggants can be perfected, and 1985 in the case of detection taggants. Backers argue that this is all the more reason to get started without further delay.