ABOUT TWO YEARS AGO this month, Igor N. Mishchenko, third secretary of the Ukrainian Mission to the United Nations, bought microfiche copies of four U.S. government technical reports at the Government Technical Information Document Depository within Columbia University's Engineering Library. During the following two months he bought copies of three more.

The technical reports cover research funded by tax dollars and available to the public from research institutions and libraries where they are stored. The reports Mishchenko bought documented progress by the National Aeronautics and Space Administration and the Los Alamos National Laboratory in designing compact nuclear reactors for defense satellites.

None of the reports Mishchenko bought was classified, but the designs and information contained in them detailed recent achievements in research on compact nuclear reactors.

It is estimated that as much as 80 percent of the information collected by intelligence agencies is not secret. Charles Yost, former U.S. ambassador to the United Nations, has written that "most significant current 'intelligence' is published in the daily, weekly or monthly press. The principal difficulty is not too little information but too much."

Three years earlier, Mishchenko's predecessor, Vladimir Demenienko, had also bought technical reports from the depository, more than 35 of them, on subjects ranging from the mechanics of robot arms used in space to radioactive waste-containment technology.

Reference librarians tend to develop their own particular stable of patrons whose research needs become familiar to them. Because I had been the reference assistant who had dealt most often with Mishchenko, he became part of my stable.

In order to borrow the microfiche reader-printer lens from the charge desk, he presented his New York State driver's license, giving his address as 136 East 67th St. The average citizen would not have had any particular reason to recognize that address as the Soviet mission. Reference librarians, however, make their living by knowing just that sort of unusual information, which placed me in an ethical dilemma: Here was a Soviet who obviously wanted to get his hands on U.S. technology, and librarians aren't supposed to restrict information or who gets it.

The next time I saw Mishchenko, he requested a copy of a report titled "Propagation of a Radio-Frequency Pulsed Signal Over the Earth." The report discussed the electromagnetic pulse generated by the air detonation of a thermonuclear warhead and the disruptive effects of such a pulse on radio and telephone communications. Mishchenko offered me "something extra" to copy it, which I declined. He seemed brazen.

I decided to call the State Department. A lawyer there said that in general it did not sound like some- thing Mishchenko ought to be doing. An FBI agent phoned me back three days later and asked me to come down to the New York Federal Building. I said I could probably make it in a few days. He said I should make it at 7:30 the next morning.

I was met by the agent who was supposed to watch Mishchenko. He was one of 350 or more agents assigned to cover foreign diplomats. I correctly identified Mishchenko from the photographs I was shown. After I had told what I knew, the agent said Mishchenko had not done anything illegal; he had been working within the 25-mile zone of maneuvering that Soviet diplomats stationed in New York are allowed, and as long as none of the documents he had asked for had been classified, he could buy copies of them.

The FBI agent said, however, that Mishchenko might ask to meet me somewhere away from Columbia: "You may find all of a sudden he'll be best of buddies with you; he'll be worried about being seen too many times and will want to move you to ground where he feels confident." If he did, would I be willing to become what the agent called an "asset?" Would I meet with Mishchenko, then tell all to the bureau?

I could walk out of the office if I wanted to, the agent said. If, on the other hand, I did decide to become an "asset," I was to remember that my own career came first and that any time I felt the matter was interfering with my own life I could say so and bow out. I bought in.

The agent's assumptions were startlingly correct. Mishchenko took the opportunity of my graduation and a new job I told him about to invite me to an expensive lunch "to celebrate." I phoned the FBI with place and time.

Mishchenko, late for the lunch, was casual and relaxed, and spoke directly of being a Soviet diplomat. He talked about his duties at the United Nations and at the mission, looking, it seemed, to see if I might balk.

We talked about my new job -- at the investment advisory company Value Line Inc. -- and our respective vacations, troubles between India and Pakistan, diplomacy and the need for better international understanding. His English was excellent and only slightly accented. American idioms gave him little trouble, and only occasionally would he slip with a stressed syllable (skiing in the Po-CONE-os).

Now that Mishchenko had "broken me away," the FBI agent predicted that the frequency of contact would drop off to roughly one meeting per month. "He has to report to his people just like I do," my case officer told me.

At next month's meeting, in a Chinese restaurant called the Chun Cha Fu on the Upper West Side (Mishchenko had a terrible time pronouncing it over the phone), he turned the conversation toward my job and the computers I used at work. He wanted to know how I spent my weekends and where I liked to travel. He was interested in my home state of Delaware, some three-quarters of which is off-limits to Eastern Bloc diplomats. He mentioned how troublesome his own family's travel and weekends were because of difficulties obtaining State Department permission for travel outside the 25-mile limit.

The FBI, which at the time was handling some spectacular espionage cases, wanted time to try to sort out what it knew. Partly to give itself this time and partly to test the depth of Mishchenko's interest, the FBI instructed me to excuse myself from the next meeting.

Mishchenko's dinner invitation came on schedule the last week in July. He accepted my excuse of having to work late that evening. "As long as he can report back that he made contact with his prospect for the month," my case officer commented, "he probably doesn't care if he actually met you or not."

My case officer went on to speculate that Mishchenko might very well tell his boss he'd met me anyway and pocket the dinner expenses. Working a prospect can put a Soviet operative on the fast track to dinners out, travel and other expenses, and a good bag of prospects shows how hard the operative is working.

MISHCHENKO CALLED AGAIN at the end of August. This time he phoned me at my office only minutes before I would have left for the day and, instead of meeting me in the usual way at a specified restaurant, he met me outside and suggested we go to a second restaurant, Nicole's, some distance away on 10th Avenue. We were the only patrons. At dinner he complained it was difficult for Soviet diplomats to meet American people as friends and, by the way, I had not mentioned any of our little dinners to anyone, had I? No. I had not thought it was any big deal.

Oh, of course not.

We talked movies, beer, Russian literature, translators, the recent Marine incident in Leningrad, the Olympics. Mishchenko said that despite the Soviet boycott, the staff at the mission had watched the Olympics on TV. He said that with all his work preparing for the upcoming session of the United Nations and for Foreign Minister Andrei Gromyko's visit, he had yet to find himself another "broker" who could help him in his research and get his reports the way I had been able to. He had been back to the library recently, but the people working there now were not as skillful or helpful to him as I had been -- had I ever thought of setting up a document retrieval business for myself? Just a thought. He could not be sure when he could get free during the next month, but it had been a good evening.

THE FBI AGREED. "I can't believe he's being this obvious," my case officer commented. On the strength of Mishchenko's hint about document retrieval, the FBI decided that the meetings were worth continuing. I was handed off to a new case officer and asked if I would be willing to take a polygraph test to reassure Washington. Again, if I said no, the whole thing would simply stop.

I cleared the polygraph test and continued to eat my way through my own version of a second Russian grain deal. About this time somebody at the Soviet mission suddenly caught on to the fact that having a prospect who worked for a major Amer-

ican investment advisory company might be valuable.

Mishchenko asked me to look around my company, particularly our library, to see what kinds of news releases, corporate earnings reports and files were stocked there. He seemed intrigued that stock investment advisory services would, as part of their assessment of a corporation's weaknesses or strengths, evaluate the personal qualities of the operating executives. He wanted to know how such seemingly private information was accessed.

I relayed this new development to my case officer who told me not to risk my job. If I needed to supply anything, the FBI would get it for me. Most of the stuff Mishchenko asked me to look for was material that the Soviet mission could have had (and very likely already did) simply by subscribing.

The FBI thought Mishchenko's requests were to evaluate my willingness to run errands. Further meetings were approved as the FBI waited for Mishchenko to give me a more sensitive task. Now that Mishchenko was meeting regularly with me, his contacts with his other American prospects had dropped off.

The major task-assignment came at the end of November. At that meeting, Mishchenko's shifts of conversational topics were more abrupt than usual, moving from casual talk to probing questions about my own work. During the meal, he put me through an embarrassing, simplistic and insulting lecture on the "benefits of the Soviet way of life" where the television newscasts always ended with a positive story item and where no one "owned anybody else." He mentioned that while he had been stationed in Vienna attending the U.N. Subcommittee on Peaceful Uses of Outer Space, he had become friendly with a consultant from either an English or a French firm (surely he knew the difference) who had had with him a thick book of helpful figures, a very expensive book; the consultant had kept it with him always, but Mishchenko had gotten to look at it during meetings. Mishchenko said he could not remember the title exactly. It went something like "NASA Space Market," by Frost and Sullivan. Would I be able to borrow a copy of it?

Frost and Sullivan is a market research company that evaluates industry reports and, using its own expertise, produces studies so comprehensive that, had the United States or any other government produced them, much of the material could have been classified.

Frost and Sullivan offered two reports similar to the titles Mishchenko had given me. These were "The U.S. Military Space Defense Market," and "The NASA/DOD Space Market," but I never got the chance to tell him about them or to let him know that I would not be able to get them for his friend. The Nov. 28 meeting turned out o have been our final one.

In January Mishchenko was recalled to Moscow, not under any obvious cloud, but it did come two years earlier than his five-year tour should have ended. Mishchenko and his wife spent a hurried couple of weeks before their departure shopping for presents such as five video recorders and cassettes of American movies. When his replacement arrived in New York, Mishchenko dutifully drove him around town for several days. Then Mishchenko sold his car and flew home.

I was relieved. My experience had been relatively benign: I was able to steer clear of both superpowers without jeopardizing my career or my country. Others haven't been so lucky.