THREE YEARS AGO, a bomb exploded at a contra camp in southern Nicaragua, close to the Costa Rican border. The explosion was apparently aimed at eliminating the then-leader of the Costa Rica-based contras, Eden Pastora.

No one has ever been arrested or brought to trial for that assassination attempt, and much of the evidence remains murky. But a civil lawsuit now before a federal court in Miami alleges that there is a connection between the bombing in the Nicaraguan jungle, in which eight people died, and some members of the covert network currently being investigated by the congressional Iran-contra committee and the special prosecutor.

The lawsuit, filed in May 1986 six months before the Iran-contra scandal surfaced, is on behalf of two American journalists based in Costa Rica -- Tony Avirgan, a free-lance cameraman and reporter who was working for ABC at the time of the bombing and was seriously injured in the blast, and his wife, Martha Honey, a stringer for The London Sunday Times. They are represented by the Christic Institute, a liberal, interfaith group previously best known for its suit against the Kerr-McGee Corp. on behalf of the family of union activist Karen Silkwood.

The Avirgan-Honey suit, which seeks $20 million in damages, alleges that 29 defendants, including retired major general Richard Secord, Albert Hakim, Thomas Clines, Robert Owen and Adolfo Calero engaged in an "on-going criminal syndicate" for the purpose, among other things, of running a private military expeditionary force in Costa Rica. The attempted assassination of Pastora, the complaint contends, was one action of the "syndicate." But the only specific allegation linking Secord, Hakim and the rest to the bombing is a claim in court papers by the attorney for Avirgan and Honey that they helped provide the explosives that were used in the bombing. The attorney's affidavit doesn't allege that Secord & Co. knew how the explosives would be used.

There is as yet no information in the suit that substantiates the contention that some members of the network conspired to kill Pastora, and all of those named in the suit have strongly denied the allegations. Robert Owen told the Iran-contra committee that the charges are "scurrilous." Calero characterized the Christic Institute to the committee as a "leftist" group with close ties to the Nicaraguan embassy in Washington.

Secord called the suit "the most outrageous fairy tale anyone has ever read" and a "minor threat." He has spent over $100,000 from his Swiss coffers on legal fees for himself and other defendants, as well as for a private investigation of Honey, Avirgan and the Christic Institute. Secord did this, he told The Washington Post last week, because he feared last year that the suit could "knock out" the secret system set up for supplying aid to the contras at the time such aid was officially banned.

Attacking the motives of the liberal Christic Institute does not answer the question posed by the lawsuit: Who tried to kill Eden Pastora and why?

The bomb explosion occurred at 7:29 p.m. on May 30, 1984 at a place called La Penca, a guerrilla camp just inside Nicaragua and close to the Costa Rican border. The camp was occupied at the time by Pastora's contra followers. Pastora was at the time the commander-in-chief of ARDE, a coalition of contra groups based in Costa Rica.

Pastora had summoned the local and international press corps earlier that day from San Jose, the Costa Rican capital, for a press conference. Night had fallen by the time the entire party had assembled, and the journalists had just begun their questioning when the bomb went off.

There's no doubt that the bomb was meant to kill Pastora, a hero of the Sandinista revolution who subsequently broke with his former comrades. Although Pastora himself escaped with burns, shrapnel wounds and broken ribs, eight others were killed, including one American. Twenty-eight people were seriously wounded, including Tony Avirgan, who suffered severe shrapnel wounds, burns and a mangled hand.

Pastora, of course, had many enemies. There is evidence that the Sandinistas may have tried to kill him in June 1983, and it's possible that they were behind the La Penca bombing, too. The Sandinistas certainly had reasons for wanting their charismatic former comrade out of the way. There are also reports that at least one rival contra leader threatened Pastora. So the Sandinistas and rival contras must be among the list of possible suspects. But Pastora's own immediate reaction was to blame the CIA.

Eden Pastora was by no means Washington's favorite contra. Although he had broken with the Nicaraguan regime, he had steadfastly refused to ally himself with the main contra faction, the FDN, on the grounds that it was dominated by alumni of the dictator Samoza's National Guard. Pastora's unbridled criticism of the right-wing contra leadership badly embarrassed the CIA, which was working hard in 1983 and 1984 to clean up the image of the counter-revolutionaries and maintain an appearance of unity. His carping wasn't exactly welcome to the FDN, either.

Pastora has stated in a deposition in the Avirgan-Honey lawsuit that the CIA paid him a monthly stipend of $150,000 when he first took up arms against Managua in April 1983. The relationship was never a happy one however, and by April 1984 the agency had suspended its aid.

At the beginning of May 1984 -- only a few weeks before the assassination attempt -- the CIA imposed a deadline of 30 days for ARDE to accept unity, according to press reports. The deadline expired on the day of the bombing. Although other leaders within ARDE were prepared to accept the ultimatum, Pastora, whose faction was militarily the strongest within ARDE, was not.

In an interview with Costa Rican radio, broadcast a week before the bombing, Pastora declared: "There are strong pressures by the CIA. And they have blocked all help to us. For the past two months, we have not received a bullet or a pair of boots. We have not received anything." In a TV interview aired just minutes before the bomb went off he again cited the agency pressure to join with the FDN. "But," he added, "the CIA will have to kill me first."

The assassination attempt itself was a highly professional operation. According to a deposition in the Avirgan-Honey lawsuit from Roberto Cruz, the attorney general of Costa Rica who supervised the official investigation, his office made a "firm determination" that the bomb consisted of C-4 explosives concealed in an aluminum camera case brought to La Penca by a man masquerading as a Danish photographer under the name of Per Anker Hansen. A Costa Rican TV cameraman actually filmed the pseudo-Dane edging away from the press conference just minutes before the bomb went off.

"Hansen" had visited Costa Rica several times since 1983, almost always in the company of a women traveling on a stolen French passport. He spent the nine weeks before the bombing in Costa Rica establishing his credentials as a freelance journalist and, according to another deposition taken in the case, scouting the site for the killing. He attached himself to a Swedish TV team working in the area (although he invariably spoke with them in Spanish and English). They thought it strange that he seemed comparatively uninterested in taking photographs, unlike other professionals, but that he was nevertheless so insistent on carrying his metal camera case wherever he went. He had curious orange blond hair and, while he travelled with the Swedes, he grew a beard. He carried large sums of cash and rarely spoke about himself.

After the bombing Hansen was treated in a Costa Rican hospital for two superficial cuts that he said were caused by the blast. These wounds do not appear in pictures taken of Hansen shortly after the bombing. At the hospital he repeatedly asked about Pastora's condition. With extraordinary coolness he gave a ten minute interview to Costa Rican radio describing, as an injured journalist, what had happened at La Penca. He disappeared from the country the next day.

In a deposition taken by lawyers from the Christic Institute, Alberto Guevara Bonilla, a former agent of the Costa Rican intelligence service (known as the DIS) testified that two months before the bombing a man he identified from a photograph as Hansen had arrived with an unidentified woman at a Costa Rican border post bearing an order signed by Carlos Monge, the director of DIS. The order directed Guevara to arrange transport for Hansen for his "journalistic tasks," a service not normally provided by DIS for visiting freelance journalists. Hansen and the woman borrowed a jeep and set off in the direction of La Penca.

The tantalizing issue raised by the lawsuit is whether any American covert operators had any links with Hansen. The evidence on this point, however, is slim. The closest the suit has come to establishing any indication of such a link comes in Guevara's deposition.

Three weeks before the bombing, according to the Guevara deposition, Hansen and his female companion turned up again, together with an American named John Hull. This time they borrowed a powered canoe and set off up the San Juan river, which leads to La Penca. On that occasion Hansen carried with him a metal camera case. The case bore a sticker that said "Fragile, U.S. Postage." A few days later Guevara was in the office of the DIS Director and saw the same case, with the same sticker.

A native of Indiana, Hull has lived in Costa Rica for over 30 years and is one of the largest landowners in the country. Most of his holdings run next to the Nicaraguan border. In his deposition in the Avirgan-Honey case, Eden Pastora, who has now retired into private life in Costa Rica, testified that the CIA station chief in Costa Rica told him after the La Penca bombing that Hull was a member of the CIA and was in charge of all CIA activities in Northern Costa Rica.

Hull's name has also surfaced during the congressional investigation of the Iran-contra affair. The hearings have produced information that he had contact with North and members of his network -- but no suggestion that Hull, North or any of them had anything to do with the La Penca bombing.

Hull has repeatedly denied any involvement with the CIA, the La Penca bombing or illegal activities of any kind and has challenged such allegations in court. He sued for libel in Costa Rica in October 1985 after Avirgan and Honey published the results of a year-long investigation into the La Penca bombing, commissioned by the Committee to Protect Journalists and the Newspaper Guild. Hull's suit challenged statements in their report that accused him of active complicity in the assassination attempt, of working for the CIA and of receiving money from the NSC.

After hearing testimony over two days in May 1986, the Costa Rican judge threw out Hull's complaint in the libel suit. Hull appealed the finding and lost again.

Meanwhile, last January, a federal judge in Miami rejected a defense motion to dismiss the Christic lawsuit and authorized the beginning of discovery in the case. The suit is expected to come to trial next spring.

As it goes forward, the plaintiffs will have to substantiate their explosive allegations in an American court. Whether they can do so remains to be seen. But perhaps the public will begin to get a clearer picture of who wanted Eden Pastora dead and why.

Andrew Cockburn is a Washington-based writer specializing in defense and intelligence affairs.