OKAY, CONSPIRACY BUFFS, try this one on for size: For the past three decades, a cadre of covert operatives known as the "secret team" has been manipulating American foreign policy to suit its own selfish political and financial designs. This conspiracy is so big that it encompasses all the little conspiracies of the last 30 years -- Nixon's anti-communist machinations in the 1950s, the Kennedy assassination in the '60s, Watergate in the '70s. This isn't just a conspiracy theory; it's a life style.

The "secret team" theory emerged two years ago from a small "public interest" legal group in Washington called the Christic Institute. The institute, which takes its name from the writings of Pierre Teilhard de Chardin, a Jesuit philosopher, is a liberal group that believes itself to be a moral and political exemplar.

While most of the moral beacons of the 1960s have burnt out, faded or even grown up, the Christic Institute's outrage burns on incandescently. And outrageously: "These guys behind the friendly face of Ronald Reagan are fascists," declares Sarah Nelson, the institute's executive director, in a recent Christic Institute colloquy. "There isn't any other word for them. I'm sorry to use that language, but there's no other word for them, and they're murderers just like the Nazis were."

The Christic Institute's genius lies in its ability to use the idiosyncracies of the American legal system to promote its political causes. The institute's general counsel and director of investigations, a Harvard-trained lawyer named Daniel Sheehan, can turn the courtroom into guerrilla theater. Sheehan initially made his name by using a suit for damages on behalf of the family of Karen Silkwood, a nuclear power plant worker who died mysteriously, to launch a crusade against the atomic power industry. (A Christic Institute brochure boasts that the Silkwood case "inspired a congressional investigation, two books, a play, several television dramas and a major motion picture.")

The Christic Institute looked for a similar legal dispute that it could use to enter the national debate over Central America. It found a plaintiff in Tony Avirgan -- a freelance American television cameraman who traveled to La Penca, in the Nicaraguan jungle, on May 30, 1984 to attend a news conference called by Eden Pastora, a renegade contra commandante. A bomb exploded as the meeting got under way, leaving eight dead and 28 injured, Avirgan among them.

In the rubble of La Penca, Daniel Sheehan found the case he was looking for. Using civil provisions of the so-called RICO law, which was drawn up by Congress to harass the Mafia, Sheehan filed a multimillion-dollar claim for damages on behalf of Avirgan and his wife Martha Honey. Named as defendants were an assortment of 29 private paramilitary operators, right-wing activists, anti-Castro Cubans, and Latin cocaine traffickers. All of them, Sheehan asserted, had participated in a conspiracy that led to the La Penca bombing. All the defendants denied the allegations, and the case was recently thrown out for lack of evidence.

Sheehan's lawsuit attracted little attention when it was first filed in May 1986. But once the outlines of the Iran-contra affair began to emerge from official sources the following November, parts of the Christic Institute's lawsuit began to appear remarkably prescient. Whether through guesswork or patient investigation, Sheehan had managed to identify several of the major participants in North's secret contra supply network -- retired Maj. Gen. Richard V. Secord, Albert Hakim and Rob Owen -- six months before anyone else had heard of them.

Reporters and official investigators in search of new leads flocked to the Christic Institute's headquarters in a block of run-down town houses on North Capitol Street. If its lawsuit was anything to go by, the institute seemed to have some remarkable sources inside North's secret world of mercenaries and arms dealers. But as the Iran-contra inquiries ploughed on, official investigators and many journalists became wary about some of the more alarming allegations made by the institute. The evidence seemed thin.

Undaunted by the lack of official interest, Sheehan continued to prepare for an apocalyptic courtroom battle between the Forces of Good, as represented by himself, and the Forces of Evil, as represented by Secord and company. And as he drummed up supporters and raised funds for this cosmic confrontation, his explanations and assertions about the background to the La Penca bombing coalesced into a wide-ranging conspiracy theory.

As presented in court documents, Sheehan's theorem maximum is that American foreign policy since 1959 has been a huge anti-communist plot. According to Sheehan, the plot began when then-Vice President Richard M. Nixon met with representatives of the Mafia gambling and prostitution syndicate that had been thrown out of Havana during the Cuban revolution and hatched a scheme for overthrowing Fidel Castro.

Together, Sheehan asserts, these unlikely partners devised a plan to train a secret band of ultra-right-wing Cuban exiles -- or "contras," as Sheehan cleverly calls them -- who would be infiltrated into Cuba to foment a counter-revolutionary uprising. Within this clandestine army was an even more secret squadron allegedly composed of professional assassins. Sheehan calls them the "shooter team" and says that in 1962 a young CIA officer named Ted Shackley and a sidekick named Tom Clines were put in charge of the "contra war" against Castro.

The shooter team, quite obviously, never completed its missions to kill Castro and his brother Raoul, and President Kennedy's Bay of Pigs invasion was a fiasco. But, according to Sheehan, the secret bands of anti-communist contras and assassins had only begun to make mischief. He contends that in 1965, the mercenary army, still under Shackley's command, was sent to Southeast Asia. There, the secret commandos allegedly teamed up with jungle warfare specialists Secord and John Singlaub in support of anti-communist Laotian tribesmen (who were also opium growers). In 1966, says Sheehan, a young Marine officer named Oliver North joined the Laotian operation.

While in Southeast Asia, according to Sheehan, Shackley and his accomplices got up to a variety of nefarious activities, ranging from a campaign of political assassinations in Vietnam to meetings with Florida gangsters and Laotian opium warlords. Sheehan adds that during a brief sabbatical as head of the CIA's Latin America division in Washington in the early 1970s, Shackley managed to mount a military coup against Salvador Allende, the Chilean Marxist. Meanwhile, according to a version of the theory outlined by Sheehan in a speech on Sept. 4, 1987, three members of the "shooter team" were among those arrested while planting bugs in the Watergate offices of the Democratic National Committee; other team members were involved in the assassination of President Kennedy.

But then it was back to serious dirty work, according to allegations made by Sheehan in court documents. Serving first as the CIA's East Asia operations chief and later as assistant deputy director of clandestine operations, Shackley (with his trusty aide Clines) supposedly stole tons of U.S. weapons from South Vietnam and stashed them in Thailand. Later, Sheehan claims, Shackley, Clines, Secord and a member of the "shooter team" named Rafael "Chi-Chi" Quintero siphoned off millions of dollars in Southeast Asia opium profits and laundered them through the mysterious Nugan Hand bank of Australia.

Still not exhausted by this tireless villainy, Shackley, Clines and members of their cabal in the mid-1970s helped Savak, the shah of Iran's secret police, to set up secret assassination teams, Sheehan claims. After Shackley and Clines left the CIA during the Carter administration, Sheehan claims that they used their training as official spooks to set up their own private "off-the-shelf" covert action squad to offer private paramilitary and espionage services to needy clients such as Moammar Gadhafi of Libya and Anastasio Somoza of Nicaragua.

The upshot of Sheehan's theory is that it was only logical for North to turn to such practiced and established operators as the "secret team" when he needed a network of secret and private operatives to supply the contras after Congress cut off their official supply of U.S. weapons. And given their alleged involvement with dope traffickers in Southeast Asia, by the strange logic of the theory, it was only natural for the "secret team" to help finance their enterprise with the profits of cocaine deals arranged with the businessmen of the Medellin Cartel.

It was the liberal magazine Mother Jones that first raised serious questions about Daniel Sheehan's theory. In a harsh take-out last winter, writer James Traub suggested that the Christic lawsuit was a "gorgeous tapestry . . . woven of rumor and half-truth and wish fulfillment" and that Sheehan was a man "in whom passion has overcome reason."

Predictably venomous attacks on Sheehan appeared in such conservative publications as The Washington Times and the American Spectator. But the liberal magazine The Nation also weighed in with a polite but pointed critique, which noted that Sheehan's theory essentially absolved successive U.S. administrations of responsibility for their own policy fiascoes.

Sheehan, through a spokesman, declined to be interviewed in connection with this article. Peter Dykstra, the institute's director of communications, said in a letter explaining why Sheehan declined to grant an interview that the group had been attacked by "a volley of McCarthy-era rhetoric and half-truths . . . ."

What a theory! Even Richard Nixon's most fervent enemies might find it hard to blame him for all the unpleasant events of the last three decades. As for Shackley, whose place as the evil genius in Sheehan's scenario was compared by Mother Jones with that of Sherlock Holmes' arch-villain, Professor Moriarty, there is no doubt he was involved in some controversial CIA actions, but under authorization from various administrations. He left the CIA in a purge of veteran officers instituted during the Carter administration. But Shackley's role in the Iran affair was marginal at most; he vehemently denies any participation whatsoever in contra supply efforts, and no evidence has emerged to contradict him.

"All the programs I was involved in were approved by congressional appropriations. They're approved governmental programs," Shackley said last week.

Despite the denials by Shackley, Secord, Singlaub et al., that they participated in the conspiracy alleged by Sheehan, federal Judge Lawrence King of Miami nonetheless allowed the Christic legal team considerable latitude to use his court's authority to rummage through the defendants' personal records and examine them under oath in preparation for "Apocalypse Now" in the courtroom.

But five days before the Christic lawsuit was due to go to trial last May, Judge King brought down the curtain, abruptly dismissing all the charges, even against defendants who had not formally moved for dismissal. The judge ruled that the Christic Institute had failed to come up with any significant admissible evidence linking the defendants to the Pastora bombing, and had failed even to produce evidence of the actual bomber's identity.

An examination of some of the file drawers full of material generated during the course of pretrial investigations shows that Sheehan had tapped into some questionable sources. The Christic Institute's leadoff witness would have been Edwin Wilson, the former CIA agent whose current lengthy prison sentence for selling arms to Gadhafi might have raised serious credibility questions.

A former CIA operative named Carl Jenkins, who Sheehan had cited as a major source for critical elements of his theory, asserted later in an affidavit for the defendants that Sheehan's description of the "shooter team" was "false," and that, contrary to assertions by the Christic Institute counsel, he had no personal knowledge of any criminal activity by Shackley, Secord, Clines, Hakim, Quintero, Singlaub or Owen.

Official investigations into Watergate, the Iran-contra scandal and the affairs of Ed Wilson have shown that certain personalities do seem to reappear with striking regularity in some of the darker events of recent American history. But there is only a limited pool of men with the skill to conduct the kind of messy clandestine manipulations that successive presidents have sometimes felt necessary; the theory that they conspired among themselves to hijack American foreign policy for their own selfish ends certainly isn't the most logical explanation of their activities.

The Christic Institute's crusade suffered a serious and perhaps decisive setback in the courts (an appeal of Judge King's ruling will take months, if not years, to resolve). But politically it still is very much alive. Sheehan has become a sought-after speaker on college campuses and at fashionable soirees; the advertised guests at one $100-a-head institute fund-raiser in Hollywood in May included such show business luminaries as Jamie Lee Curtis, Ed Begley Jr. and Carrie and Rob Reiner. (It isn't known whether any of them actually turned up.) The institute reportedly takes in thousands of dollars in contributions each week and sells a catalog of inspirational videotapes, audio cassettes and literature.

The Christic lawsuit has inspired at least two volumes of nonfiction, and its ruminations also seem to have provided story lines for several prime-time television dramas (including episodes of "Miami Vice" and "Wiseguy"). Sheehan and his crusade were even discussed reverentially on an episode of "Cagney and Lacey." Of such media exposure modern myths are made.

In the end, true believers in the "secret team" are unlikely to be persuaded by court judgments or journalistic investigations that the theory is untrue. After all, an authentic conspiracy theory has no difficulty responding to criticism: The critics are part of the conspiracy. Mark Hosenball is a Washington correspondent for the London Sunday Times.