A mysterious Israeli tycoon and the Mossad, Israeli's intelligence service, appear to have provided Idi Amin's Uganda Airlines with its two Boeing 707 jetliners as part of an Israeli effort to spy on Libya.

The planes, which fly cargo between Uganda and Europe, make refueling stops several times a week at the military airport at Benkhazi, Libya. These visits to Libya, according to a source in the intelligence community here, are at the heart of this peculiar affair.

Sources say that "navigators" who accompany the planes' regular crews file reports that are later shared among Israeli, British and U.S. intelligence.

The operation, according to intelligence sources, yields few if any secrets of value. The sources here also believe that nobody is fooling anybody in this affair.

But Idi Amin must be delighted with a cut-rate service that transports Ugandan coffee, officials and their mistresses to Europe and brings back whiskey, machine tools, live stock, and Mercedes Benz limousines.

Intelligence sources here suspect that Libyan leader Col. Muammar Quaddafi also likes the idea of knowing what planes spies will be arriving on. The sources assume that Qudadafis agents provide Libya's visitors with appropriate "disinformation."

But the big winner in this operation appears to be Shaul Eisenberg, the clusive Israeli entrepreneur at its center.

The two used Boeing 707s - which together with a used Lockheed C-130 comprise Uganda Airlines - got to Amin through several of Eisenberg's 80 or so companies.

The chief Eisenberg firm in these deals was Aircraft Trading and Services Inc., or Atasco. Headquartered in Asia House, Eisenberg's luxury building in Tel Aviv, Atasco also has branches in the "Eisenberg Building" in New York and in London.

Atasco was put together in 1971 by executives of Israeli Aircraft Industries, a wholly owned subsidiary of the Israeli Defense Ministry that makes planes and missiles.

Eienberg got into Atasco as an equal partner with Israeli Aircraft for $500,000 in cash. After the 1973 Middle East War, Israeli Aircraft, staggered by scandals, sold its share in Atasco to Eiseberg, leaving him its sole owner.

The rest of Atasco's original capital, $5 million, came from the U.S. Export-Import Bank, which is supposed to make loans to promote American exports.

The Ex-Im Bank certainly found the right man in Eisenberg. He quickly turned into an eager customer for Pan American Airways' used Boeing 797s.

Atasco bought 12 or 15 of the advances series "C" 707s that Pan Am was selling and purchased six out of ten earlier series "C" 707s being sold by the airline.

At its Israeli hangars, currently jammed with 707s bearing obscure markings, Atasco remodels the interiors to suit customers and paints on their proud colors - Iran Air, Tarom of Romania, Uganda Airlines.

In May 1976, Atasco sold the 707 that was once Pan Am's "Clipper Jupiter" to a firm in Zurich, which dealt it on the Amin.

Intelligence sources say that the head of this Zurich firm is a 15-year veteran of Mossad, the Israeli intelligence agency, and the firm is an agency, and that the firm is an agency "laundry." It exists, these sources say, to pass on Mossad funds for deals in which the Israeli secret service is interested.

By the time somebody decided in 1977 that Uganda Airlines should double its 707 fleet, the Carter Administration had taken office and the State Department was examining all export licenses to see if the product might be used in the suppression of human rights.

Since it seemed unlikely the sale of another 707 to Uganda would be approved, Atasco sold the plane that once flew as Pan Am's "Clipper Undaunted" to something called Ronair Inc., which then leased the 707 to Uganda Airlines.

Ronair - three people and President Fred Solomon - by remarkable coincidence shares an office with Eisenberg's Atasco in the Eisenberg Building at 4 E. 39th St. in New York City. Nobody at Ronair would talk to the Washington Post.

Since Amin, when he seized power, killed most of Uganda's trained pilots, his airline was short of crews. So to fly his 707s, Amin - or his suppliers - turned to a U.S. firm, Aviation Technial Assistance and Service Co., or Avtec, of Burlington, Calif.

This firm, which supplies air crews, is said to have no formal intelligence links. Its president, John McEvoy, initially told a reporter who called on him at Avtec's London office, that he could not remember who had brought him the Uganda Airlines contract. Then he remembered it was the Swiss firm.

Under questioning, he finally acknowledged that "we're a subcontractor" of the Swiss firm.

McEvoy was also certain that his firm had no ties with Eisenberg's Atasco. However at least one pilot hired by Avtec to fly for Uganda Airlines recalls that his training on the 707 was held up for lack of a $15,000 payment. This pilot simply called Atasco in Tel Aviv to pay Avtec's debt and the money arrived promptly. McEvoy said he thought there had been some mistake.

While McEvoy's firm supplies the pilots, however, it does not supply Uganda Airlines with navigators. Indeed, pilots assert that none are needed on the Uganda Airlines planes.

However, several have been spotted by other air crews. Intelligence sources here say it is the "navigators" who do the looking when Ugandan planes call in Benghazi, Libya.

Whether they see anything worthwhile is doubted here.

One of the most fascinating figures in this whole afffair is Eisenberg, the Yaddish-speaking tycoon who never speaks with the press.

In Israel, much is known of him, however. He was born in Munich in 1926, somehow got to Japan and there married the daughter of an Austrian painter and his Japanese wife. Eisenberg is thought to have sat out the war years in Japan.

After the war, like several other fabled international operators, Eisenberg started his fortune by dealing in surplus weapons. He prospered. His family multiplied. So did his corporate entities.

Today he boasts comfortable homes in Tokyo, London, Zurich and Savyon, a wealthy suburb of Tel Aviv. Four of his married daughters live in Israel. A fifth lives in a villa at Hampstead, London's version of Cleveland Park.

Eisenberg himself maintains an apartment there in a substantial building nearby. Two floors below him live his Erwin and Erwin's wife. The Hampstead Eisenbergs are as untalkative with a reporter as are those in Israel. Like Eisenberg's various aides, his family profess never to know where he is or when he will be back.

Eisenberg's business empire, which operates all over the globe, includes at least 70 concerns in one holding company alone, United Development Inc. Atasco is one of the United's subsidiaries.

Outside United's grasp is Eisenberg's Eisenberg Export Co., Bargad Trading Co., Asia House and others.

Eisenberg is clearly a persuasive man. He is the sole beneficiary of what in Israel is called "the Eisenberg law." It exempts from tax certain companies who do business abroad. So far, it fits only Eisenberg.

Israeli experts say that a contribution of 10 million Israeli pounds for a hospital in Jaffa helped create a favorable political climate for enactment of the law.

It is not clear what nationality he really is. One report says he carries an Austrian passport. But Eisenberg is obviously earger to keep close to Israel's power elite. He staffs his companies with high-ranking former officers, diplomats and the like.

At the Israeli Aircraft Industries hangar where Atasco work is done, Eisenberg is currently outfitting one of his 707s for his own use. It will serve as a flying office to keep him in touch with his business world, more or less coterminus with the planet.

A recent and vain call to Atasco's London offfice turned up the report that Eisenberg was in Hanoi, "negotiating a big deal."

He does not always take all branches of the Israeli government into his confidence. When the late finance minister, Pinhas Sapir, first learned of Eisenberg partnership with Israeli Aircraft in Atasco, Sapir remarked: "We were shown a bride who is slightly pregnant."

But Eisenberg obviously has a charm that overcomes resentment. It was Sapir who pushed through the "Eisenberg law."

There are frequent but unsubstantiated reports that Eisenberg operates mostly from Central America these days. Among other things, he is the Panamanian honorary general consul in Tel Aviv.

Like Eisenberg, the Mossad could not be reached for comment on this affair. Israel, like Britain, pretends its intelligence services does not exist.

As for the putative Mossad man in Zurich, his secretary said her boss was unreachable, "on a boat."