For nearly a year, a tantalizing story has been unfolding about a purported Libyan plot to procure the release of eight C130 transport planes roosting on a Georgia runway.

The story involves Libyan diplomats working with American felons and influence-peddlers to free export licenses, withheld by the U.S. government because of Libya's record of aiding terroritsts. All the elements of a block-buster are there: Libya's alleged willingness to fork over $15 million in bribes, a $1.5 million public relations front, a "good-will" slush fund of $400,000.

Newspapers as far away as Sweden, syndicated columnist Jack Anderson, magazines and television have carried the story with its dark hints of corruption -- made even more sensational by recent developments involving Billy Carter and intimating that the corruption may reach as high as the White House.

There's only one problem with the story: No one knows how much of it is true.

The prime sources of the story are less than sensational. Some, in fact, are trusted by no one. Robert L. Vesco, for example, the self-exiled financier and reputed brians of the comspiracy, who fed pieces of the story to the media from his home in the Bahamas. A much richer lode, now and for probably months to come, is 61 covertly made tape recordings -- a thicket of factual nuggets, purest malarkey and ugly, unsubstnatiated and vehemently denied acusations.

The tapes were turned over to federal prosecutors in Manhattan by James W. Feeney, who was a wired undercover informant for them, and who is also a thrice-convicted swindler.

An exotic cast appears in the tapes. The names, spoken by Feeney, Vesco, at least two other convicted swindlers, and Libyan diplomats, include Billy Carter and JohnC. White, chairman of the Democratic National Committee.

A brief tape segment, recorded by Feeney is his New York City apartment, is said to be from a phone conversation in February 1979 with Vesco intimate James C. (Jimmy) Day Jr., a former Texas state representative (1957 to 1961) who, two months later, pleaded guilty in federal court in Houston to making false statements to financial institutions and drew a two-year suspended sentence. In the tape segment, Day imputed misconduct to a high government official who wasn't named.

Last week, aides to Sen. Orrin G. Hatch (R-Utah) played the segment for ABC televison, The New York Times, The Washington Post, and possibly others in the press. They also permitted examination and note-taking on a summary prepared by Thomas P. Doonan, a criminal investigator for the U.S. attorney in New York, on Feeney's report on a June 30, 1979, meeting in Washington in which the participants were Day and two emissaries of Libya. Day gave a tape of the conversation to Feeney.

Hatch, in a phone interview, said he wanted, no dissemination of unsubstantiated allegations, but thought reporters should be able to sample for themselves the technical "quality" of the tapes. The quality of the segment was excellent.

The obviously sensitive tapes -- raw files with a high potential to besmirch the reputations of possibly innocnet persons and even to affect the presidential election campaign -- had been closely husbanded by federal prosecutors for an investigation that began 19 months ago and has involved formal presentations to a grand jury since last fall.

Recently, however, Doonan, the criminal investigator, removed the tapes from the vaults of the U.S. attorney, duplicated them and took the copies to Colorado. This was the first leg of an unusual journey in which the last stop was Capitol Hill.

Doonan delivered the copies to a secret pretrial proceeding in Denver, where Feeney and two codefendants were facing trial on federal charges of wire fraud, mail fraud and interstate transportation of false securitites.

In the pretrial proceeding, Feeney contended that the tapes and 75 related exhibits constituted his defense and therefore should be available to him at trial. The government aruged for suppression. Judge Sherman Finesilver agreed with the prosecution, bound lawyers at the hearing to silence and sealed the tapes and exhibits. On July 28, Feeney and the two other men were convicted of 16 counts.

Three days before the verdict, Feeney summed up what he says is the contents of the tapes in a long interview with Kurt Karlsson, the American correspondent of Expressen, a Stockholm daily. Karlsson, whose story was published July 27, has known Feeney for some time.

Meanwhile, Sens. Dennis DeConcini (D-Ariz.) and Hatch, leaders of a Senate Judiciary subcommittee probe into possible ties between Vesco and government officials, interviewed Vesco in Nassau, his longtime Bahamian refuge from outstanding fraud and other indictments. Vesco tipped the legislators to the existence and whereabouts of the tapes and exhibits, depicting them as potential bombshells.

DeConcini then signed a subpoena to get the materials from Chief U.S. District Court Judge Fred M. Winner, who had temporary custody of them. Winner set off shcok waves in the Justice Department, a reporter was told, by releasing the materials without notifying the department or holding a hearing. The judge declined to comment. "It's too complex to try to explain," he told a reporter.

The tapes and exhibits were fetched from Denver by minority counsel Thomas D. Parry, because, as the husband of an airline stewardess, he enjoyed sharply discounted air fares. This minor economy guaranteed expedited delivery to Hatch, whose staff began the very night of Parry's return, Aug. 5, to transcribe and review the materials. Somehow, it also led to a piecemeal transfer, lasting more than a week, of the materials to the irritated staff of subcommittee chairman DeConcini.

All of this caused anxiety and consternation in the Justic Department, where the FBI and the Public Integrity Section -- the subject of a continuing subcommittee inquiry -- had participated in early phases of the investigation into the alleged Libyan conspiracy by the prosecutors in New York.

In an anxious letter to DeConcini last Tuesday, Deputy Attorney General Charles B. Renfrew warned aginst public disclosure of the materials. Terming them "important ingredients" in the "ongoing grand jury investigaton" in New York he said their release "would . . . seriously impede the investigation." He added:

"In fact, should certain witnesses prematurely become aware of the contents of these materials, particularly the tapes, our attempts to develop a prosecutable case could well be thwarted . . . I earnestly request that this material be closely held by the committee and, if you feel that hearings must be held on this matter, that such hearings be in executive session."

A similar plea to DeConcini was made from New York by U.S. Attorney John S. Martin. He told a reporter: "The decision whether or not to bring any prosecution will be based on the evidence and nothing else. We are pursuing the investigation."

Feeney's effectiveness as an undercover informant and the validity of some of his materials aren't disputed. At one point, he flew to Nassau, covertly taped Vesco, and brought back a trophy authenticating his vist: a coffee cup bearing Vesco's fingerprints.

Moreover, Feeney's 57 cassettes and four tape reels include conversations about the alleged conspiracy with Libyan diplomats, including Mansur Rashid Kikhia, Libya's ambassador to the United Nations: Ahmed Madfai, formerly charge d'affaires in Washington and Ramadan A. barg, second secreatry at the People's Bureau here.

Feeney secretly recorded a conversation in New York with Kikhia. His access may have been arranged by Vesco, who claims close financial ties to Libyan leaders.

Sources say it's never been established whether the Libyans -- even if willing, eager participants in the alleged conspiracy, as claimed by Feeney -- were themselves targeted for a swindle. "That's the real question," one source said. "Who's being conned here?"

Repeated requests by The Washington Post for comment from Libyan emissaries here and in New York were unavailing. Last Monday, however, Kikhia told The New York Times that while Libyan diplomats listened to the public relations proposal, they committed no money. He strongly denied that any Libyan oficial had entertained the idea of authorizing or making bribery payments. Payments to persons who aren't public officials wouldn't be bribes.

According to the Feeney materials, a $1.5 million public relations front, to be based in Washington, was to be a conduit for $15 million in payoff money, which was to be drawn from bank accounts the Libyans would set up in Europe. The founding fathers of the operation, each to be paid $120,000 a year, were to be Vesco, in the name of his Bahamian-chartered Mexicali Investments Ltd.; Feeney; Day and an associate, James Wohlenhaus.

The alleged conspiracy used code names. That for conspiracy used code names. That for Democratic National Chairman White was Blanco, for Libya, Sandbox, and for Vesco, the Vicar.

About a year ago, White talked with Kikhia in a totally public place, the rooftop terrace of the Washington Hotel here. FBI agents photographed the meeting, first reported by The times last Sept. 30.

This is one of those factual muggets, the kind that are subject to multiple plausible, but incompatible, explanations.

Day and Feeney, of course, cast White in a conspiratorial role -- but the evidence to support their allegations, from any source, is understood to add up to zero.

White, also as would be expected, has repeatedly asserted complete innocence of any impropriety. In one of two phone interviews, his counsel, Staurt F. Pierson, repudiated any suggestion that White was "in any way connected" with a scheme to buy or peddle influence on behalf of the Libyans. "Preposterous." he said." Absolutely and totally false."

As a political leader, it was routine for White to have met with Kikhia because a request to do so had come from Jimmy Day with whom, Pierson said, "he has been acquainted . . . for a number of years, principally as a result of Mr. Day's wife's involvement [with White] in Texas politics."

If either Kikhia or Day had any connection with Vesco, White did not know of it at the time, Pierson said.

Last October, White appeared voluntarily before the grand jury. He said at the time that he understood he was not a target of the investigation. From the grand jury itself, only silence has emanated.

In past press interviews, White has said that Day had asked him to meet with Kikhia, who was seeking help in getting an appointment to meet President Carter to talk about Libyan-American relations and the release of the C130s, and that he granted Day's request as a "courtesty."

White said he refused to try to arrange the meeting with Carter that the ambassador had requested, suggesting instead that the State Department be contacted. "He would not say publicly whether he himself had been to touch with State Department officials," The Times said in its September story.

At the time Feeney agreed to become a wired undercover informant, he was facing criminal fraud charges in U.S. District Court in Brooklyn. His willingness to cooperate with the federal prosecutors in Manhattan was reported to the trial judge, and, last Dec. 27, his sentence to two years in prison was suspended. By contrast, Feeney claimed to foreign correspondent Karlsson that in exchange for his cooperation, he had been promised a sweeping immunity for unrelated offenses, but that the government treacherously had reneged.

For an investigation of Vesco, Feeney was a natural. Although "I didn't know him well, I knew him like a lot of people that sold securities,' Feeney told Karlsson. "His attorneys in Switzerland were my attorneys. His banker in Switzerland was my banker."

More importantly, he had been approached by James W. Brewer, whom he described to Karlsson as "a broker, a financial broker and insurance broker." Court records, however, describe Brewer as yet another convicted swindler who, like Feeney and Vesco, has been the target of numerous fraud actions by the Securities and Exchange Commission.

As Feeney recalled it, Brewer wanted him to put up $50,000 "to help finance a program," meaning the preliminary arrangements for the alleged conspirary to free the bought-and-paid-for C130s from a Lockhead Aircraft runway in Marietta, Ga.

Feeney said he refused to consider the investment "until I meet Bob Vesco and I know he's involved and he tells me with his own words that truly what you're speaking about can be one. So he makes arrangements and I fly down to meet Bob Vesco."

Returning with the fingerprinted coffee cup, he was asked by impressed federal prosecutors to phone Vesco in their presence and let them tape the conversation. Feeney agreed. "I dialed Vesco and I started talking with him," he told Karlsson. This is another undisputed nugget.

Truth may never be more elusive than when entrusted to the dazzling persuasive skills of superb con artists. "I made my peace with Bob Vesco," Feeney told Karlsson. "Now I have Bob Vesco on my side, working with me to tell the truth."