Some of the U.S. aircraft industry's most precious technologies are processes for using a new generation of strong, lightweight plastics to replace metal in airplane bodies.

But in 1980, the Defense Department turned aside Air Force concerns and decided to let Mitsubishi Heavy Industries learn some of the secrets for using materials in the speed brakes of F15 fighter-bombers being built by Mitsubishi in Japan.

The Navy and Air Force also have argued that computer software for the AIM9L Sidewinder missile carried by the F15 is too sensitive to share even with allies, because of the impact on U.S. security if Soviet spies obtained it.

But Defense authorized Raytheon to transfer AIM9L production data to Mitsubishi and a German-led consortium in Europe.

In the mid-1970s, NASA spent tens of millions of dollars developing the Quiet Short Haul Research Aircraft, an experimental plane that cycled its jet exhaust back across its wings for extra lift.

According to the White House Office of Science and Technology Policy, Japanese companies acquired NASA's public papers on the plane, including a Boeing report that was to be restricted to U.S. agencies. They used the the papers to produce their own experimental, short-takeoff plane.

Those incidents, all of which have enhanced the technical capability of an already expanding Japanese aircraft industry, are at the heart of a spreading controversy in Washington about whether the United States has given away information vital to its security and commercial competitiveness.

Under fire are liberal policies on sharing technology during the Carter administration, which justified them by citing a need to help Japan attain its defense commitments.

In a study published in March, 1982, the General Accounting Office said that the Carter administration's agreement of June 20, 1978, to allow Japan to build 100 U.S.-designed F15s for its Air Self Defense Force "supported Japan's strategy to develop a world-class aircraft industry."

A preliminary draft of a report by the president's Cabinet Council on Commerce and Trade contended that " military co-production has had an adverse commercial effect for the United States in a number of cases."

One U.S. official put it far more bluntly:

"We've been using the crown jewels of technology to get a country, Japan, to defend itself even though that should be in its interest, and in the process we've undermined our own industrial base and taken work away from our own defense contractors. We've taken the view that turning the spigot of technology on to accommodate our allies was a price worth paying. It's been a dangerous and irrational policy." Generosity Begets Competition

Japanese government officials and businessmen readily acknowledge using U.S. military co-production deals to help thrust Japan into the big leagues of the global commercial-aircraft industry, which has "significant technical influence on other industries," as one Japanese government report noted.

In the F15 case, the Air Self Defense Force is paying civilian defense contractors $1.8 billion more to acquire manufacturing processes and components needed to build 100 of the planes than it would have cost the Japanese military to buy them "off the shelf" in the United States.

Conflicting pressures and views inside and outside the U.S. government are propelled by concerns beyond the monetary costs of a weapons system.

Diverse interests in the F15 case include the foreign policy and strategic goals of the State and Defense departments, defense contractors' desires to sell aircraft in Japan, the armed services' fears that critical technology could leak to the Soviet Union, Commerce Department fears about strengthening foreign commercial competitors and the U.S. special trade representative's doubts that this country is receiving enough technology in return.

"It gets very tricky," said Roger Winblade, manager of NASA's subsonic aircraft office. "Other countries have extensive research activites. If we were to be too heavy-handed in limiting what others could have, we could hurt ourselves. Technology is so international today that trying to compartmentalize it is very difficult. It's a very delicate balance."

In a sense, the conflicts inherent in controlling the flow of U.S. technology abroad are built into the confusing maze of scattered and often seemingly contradictory regulations and laws.

NASA's charter, for example, requires the agency "to provide for the widest practicable and appropriate dissemination of information concerning its activities," including large amounts of aerospace research and development useful to other countries.

The Commerce Department's National Technical Information Service annually distributes about 80,000 papers containing results of federally financed research. The service is available to foreign countries, including those in eastern Europe, and was available to the Soviet Union until February, 1980, when President Carter canceled the subscription in retaliation for the invasion of Afghanistan.

Commerce maintains a lengthy "commodity control list," composed of sensitive products and processes that could be used for either military or civilian purposes.

Under the law, companies exporting these products to some non-communist nations need a validated license in which they stipulate that equipment or production data will not be diverted to the Soviet Union.

The requirement excludes goods shipped to Canada, which has at least 13 communist-owned but Canadian-chartered companies, some of which may be acquiring U.S. defense-related technology, according to a report of the White House science adviser. U.S. Lists 'Critical' Technologies

The Export Administration Act of 1978 tried to clarify this issue by requiring the executive branch to draft a list of "militarily critical" technologies. This exercise has proved far more complex than was foreseen, because it affects hundreds of companies.

The Pentagon's first attempt to draw up such a list in 1980 became a 700-page document that was highly classified on grounds that the list could provide a mountain of useful information to the Soviets. A National Academy of Science panel said it needed "drastic streamlining."

However, one of the most glaring technology "leaks" is acknowledged by Reagan administration officials to be the Pentagon's previous desire to provide large amounts of technology to allies as an inducement to purchase U.S. weapons.

In return for buying a U.S. weapons system, foreign countries have been authorized by the Pentagon to build part of the system. That often involved acquiring from U.S. defense contractors the technical knowledge to produce very sophisticated equipment, including missiles and aircraft.

In 1975, the Ford administration signed an agreement with Great Britain waiving traditional "buy-national" requirements. Under the Carter program, such agreements were signed with other NATO allies to create "rationalization, standardization and interoperability" (RSI) of NATO equipment.

On June 29, 1978, Jean A. Caffiaux of the Electronic Industries Association warned a House Armed Services subcommittee that military co-production understandings being "secretly negotiated" by the Pentagon "may have the effect of committing U.S. industry to deals that are unwise, unfair and could require the surrender of technology to foreign competitors without adequate compensation or safeguards."

Former associates describe William J. Perry, then undersecretary of Defense for research and engineering, as a fervent advocate of sharing technology to promote the "inter-operability" of allied military equipment. On Nov. 10, 1978, for example, he wrote a memo complaining that the program lacked "full effectiveness" because of the "inability of foreign countries to gain access to . . . technical data relating to acquisition programs."

On March 5, 1980, a Defense Department directive advised that Pentagon agencies "shall encourage the transfer of technology" to allies and should "foster an early mutual exchange of technological and other information with NATO allies to promote the development and adoption of standardized or inter-operable weapons systems."

"The Defense Department was put in a position of fearing to defend critical technology," a Pentagon source said.

One side effect of these Carter administration policies toward NATO was to encourage an aggressive Japanese push for some of the same access that Europeans were getting.

Perry, now with the San Francisco venture capital investment company of Hambrecht & Quist, declined to be interviewed for this series. The Pentagon has denied, on national security grounds, repeated requests by The Washington Post over a four-month period to examine the Japan-U.S. F15 agreement, the report of the Military Information Disclosure Policy Committee that evaluated Japan's ability to keep top technology secrets, or any other documents connected with the deal.

Privately, however, The Post was told that a major reason for the denial was concern that such information could embarrass the Japanese government, which is facing domestic criticism for its planned arms buildup. F15 Program Caused Tension

From the beginning, the F15 program aroused sensitivities on both sides of the Pacific.

Soon after the June, 1978, "memorandum of understanding," Air Force specialists at the Pentagon and Wright-Patterson Field in Dayton, Ohio, drew up an extremely detailed list of technologies considered too sensitive to be transferred to Japan because of the danger to U.S. security if they fell into Soviet hands.

Nicknamed the "negative list," it was obtained somehow by officials at Japan's Ministry of Defense, according to V Garber, who worked for Perry as director of international programs.

Garber said the list apparently was passed to the Japanese by someone at the Defense Security Assistance Agency. In any case, he said, when he and Perry traveled to Japan in late 1978 they were greeted with "indignant demands" that restricted F15 technologies be released. Japanese officials argued forcefully that without these technologies it would be difficult for them to make repairs, Garber said.

Garber, now at NATO headquarters in Brussels, said in a telephone interview that it was "most unfortunate" that the Japanese obtained the detailed list. But once they acquired it, it was deemed necessary to soothe ruffled feelings.

"I told the Air Force what the Japanese demands were and asked them to review the list now that we had a more unhappy situation vis a vis Japan," he said.

Garber denies that "Perry or I overrode the Air Force," but Air Force sources remember this as a time of extreme pressure from Perry, Garber and the Japanese.

"The RSI banner was waving, and the bugles were blowing," one Air Force officer said later. Firms Cleared for Licensing

Air Force sources are also critical of the failure by Perry and Garber to establish a ceiling on what amount of the plane could be built by Japanese companies, thus departing from procedure followed in the European F16 co-production program. According to McDonnell Douglas, work done in Japan accounts for more than half of the value of the Japanese F15s.

The absence of a ceiling cleared the way for a massive flow of military technology to Japan.

Virtually every big name in U.S. defense contracting was cleared after 1977 to license designs and manufacturing processes to Japanese companies in connection with military co-production. They included United Technologies, Honeywell, TRW, Rockwell, Texas Instruments, Goodyear Aerospace, Litton, Teledyne, General Electric, Itek, Motorola, Raytheon and Sperry.

Although the Air Force prevailed in opposing release of such highly sensitive technologies as design criteria for the gyroaccelerometer in the inertial navigation system--adaptable, the Air Force said, to ballistic missiles--it failed in trying to keep some of McDonnell Douglas's composite materials know-how out of the hands of Mitsubishi, the F15 program's prime contractor.

"Composite materials," a family of strong plastics that includes Fiberglas, kevlar and carbon-graphite fibers, have begun to revolutionize the aircraft industry.

Although aircraft designers still are learning how to exploit these materials, they soon are expected to extend the range of planes and missiles, add thousands of hours to the flying life of jet fighter-bombers, make possible exotic new airplane and helicopter designs, save fuel and resist radar detection.

Although only about 3 percent of the weight of Boeing's new jetliners is made of composites, the company estimates that this could rise to a "minimum" of 65 percent by the year 2000.

Japanese companies are considered the leading producers of these materials, but U.S. aircraft companies are ahead in the critical technology: knowledge of the properties, bonding techniques and applications.

"The materials are common to the industry," a Boeing executive said. "It's how you use them that makes the difference."

According to military sources, the Japanese military was adamant about obtaining McDonnell Douglas' designs and procedures for building the F15 speed brake out of carbon composites. The Air Force, citing the company's "highly perishable" lead, was opposed. So strong was the Air Force's opposition that it was not until early 1981, more than two years after the F15 deal was approved, that the government finally authorized release of the technology.

Japanese executives acknowledge that this technology has been valuable to Japan's commercial aircraft industry. In an interview with The Wall Street Journal published last Nov. 26, Mitsubishi Heavy's chief engineer, Akira Ikeda, said his company's F15 work was teaching it "many things" about composites useful in future airliners.

Ikeda also noted that wing-bolting techniques and rubber fuel tanks on his company's Diamond One business jet, now being sold in the United States, were developed as a result of previous military co-production projects. Security Raised Concerns

The Air Force's concern about the security implications of the F15 deal increased in late 1978, when Koku Journal, a Japanese aviation magazine, published a 200-page special edition on the F15 that included dozens of color photographs, charts and diagrams. The publication sparked a brief investigation by the Air Force's Office of Special Investigations, which concluded that the information had come from "technical orders" furnished by McDonnell Douglas and the Commerce Department.

The difficulty of separating military and civilian programs is evident at Japan's main aircraft works in Nagoya, where civilian and military programs proceed side by side. A Nagoya-based aircraft consortium that includes the F15 prime contractor, Mitsubishi, is at work on a major commercial project, building fuselage parts for Boeing's new 767 jetliner.

Public and private officials involved in the F15 program nevertheless question whether any unduly sensitive technologies were in fact transferred to Japan in the pressure of the moment.

Garber, who recalls the differences of view with the Air Force over releasing composites, says that in retrospect he does not believe the decision to share the know-how was "really regrettable--it wasn't the latest technology."

McDonnell Douglas spokesman Timothy J. Beecher said the company was on the sidelines for the decision on composites.

"It was between the two governments," he said. "But we think it's valid to ask the people who made the decisions whether countries involved could not have obtained those technologies elsewhere."

By the time the carbon fiber technology was released to Mitsubishi, he noted, the commercial aircraft consortium in Nagoya was making landing gear and wing edges for the Boeing 767 out of composites and using procedures supplied by Boeing.

A Boeing official acknowledged that, under the commercial program, the Japanese are using Boeing specifications and design information for the plastic composite kevlar but not for carbon fibers, considered more advanced.

"The Japanese would have loved to have had all our fancy computer programs on how we put wings together," said H.O. Withington, Boeing's vice president for engineering. "But we guarded that pretty carefully. As far as giving away the store, I don't think we've ever given anything that wasn't available to anybody who wants to take the trouble to do it." Impact of Co-Production Studied

Under the Reagan administration, concern about U.S. technology losses has increased dramatically. The impact of co-production programs is being studied by NASA, the Treasury Department, the Defense Science Board, the president's Cabinet Council on Commerce and Trade and the White House Office of Science and Technology.

Some aircraft specialists suggest that the debate over U.S. technical aid to Japan's airframe industry may be overtaken by developments that have made more technology sharing inevitable in the global aircraft business. It now seems likely that a Japanese consortium will become a full partner later in this decade with either Boeing, McDonnell Douglas or Europe's Airbus in building the next-generation jetliner, a fuel-efficient 150-seater.

Despite the massive flow of military technology to Japan, the U.S. government has not gained assurances from the Japanese government that specific technologies will be released to U.S. defense contractors in return.

Japanese officials have pointed out that Japanese law prohibits export of defense equipment--a broad category that could include many processes and materials if the Japanese wanted it to.

But Stephen Piper of the special trade representative's office says Japan "should not hide behind a weapons export ban . . . . If we tried, we could identify basic Japanese technologies which are basic to us."NEXT: Is America Inc. the answer?