The Navy's secret hostage rescue team, Seal Team Six, is the subject of a wide-ranging investigation of financial misconduct that so far has resulted in the federal indictment of one former member and court-martial guilty pleas by two others on theft charges.

The former Seal is charged with falsifying travel and training vouchers and stealing a $3,800 piece of scuba diving equipment in 1983 and 1984. The two others confessed to stealing several thousand dollars in 1985 and 1986.

Investigators have been focusing on expenditures of training and procurement funds, sources said, and no evidence is known to have been found linking any thefts to the team's operations. But investigators are examining what one called "a roomful" of records and documents dealing with millions of dollars of expenditures by the team since it was formed in 1980.

Little is publicly known about Seal Team Six because its counterterrorism mission is classified. But knowledgeable sources said it was sent to Grenada during the U.S. invasion in 1983, and dispatched to the Middle East during the 1985 hijacking of the Achille Lauro cruise ship.

The sources said some team members were on the ground in Beirut during the same period as part of the search for CIA station chief William Buckley, who was kidnaped and later killed by an Iranian-backed group.

In addition, the Navy is investigating a separate incident in which several former members of the unit and its original commander are being sued in federal court in Los Angeles by a civilian security officer. He alleges he was kidnaped and beaten by an overzealous special Navy security unit, code-named "Red Cell Team," during a training exercise to test vulnerability of a Navy weapons storage depot to terrorist attack.

In his suit, Ronald D. Sheridan, 52, a security officer at the Seal Beach, Calif., Naval Weapons Station, south of Los Angeles, said he had been told ahead of time that the mock terrorist attack would take place. But he was not prepared for what happened.

He said he was stripped, kicked and beaten by members of the team while a camera crew recorded some of the episode. He also said the team stuck his head down a toilet while flushing it several times and repeatedly dunked him in a bathtub filled with water. The lawyer for the head of the Red Cell security team said his client took no part in the alleged attack on Sheridan.

The continuing Navy and Justice Department financial investigation of Seal Team Six started in late 1985. It mirrors one that recently rocked secret Army special operations units, including its hostage rescue team, Delta Force.

Like the earlier Army probes, the Seal Team Six inquiries raise questions about the accountability of millions of dollars in secret funds expended by the special counterterrorism units set up in the wake of the Iranian hostage rescue debacle in 1980.

Those inquiries also raised numerous questions, many still unanswered, about the rules by which such secret groups operate, and whether covert units can, or should, be held to the same standards of accountability as regular forces.

"You can't create special units and then, in a fit of exasperation, let them run on their own. That's the services' attitude," said one former Pentagon official familiar with the units. "Without leadership anything can go wrong and the least of the reasons is venality. There are questions of accountability all the way up the line."

Navy officials declined to discuss Seal Team Six's secret counterterrorism mission. But knowledgeable sources said four members were drowned in a mishap during the invasion of Grenada when they were parachuted into high seas in darkness.

Seals -- an acronym for sea, air, land -- are Navy commandos trained in underwater demolition and sharpshooting. Seal Team Six, composed of some 200 commandos and support crews, picked as the best of the already elite Seal teams, is based in a closed compound at Dam Neck, Va., near Norfolk.

Capt. Charles E. Ellis, chief legal officer for the Norfolk command handling the military probe, said in papers in the court-martial of Seal Team Six intelligence specialist Chuck Voyles last April, "It appears that the accused was caught in an atmosphere of thievery and fraud practiced by others within the command. The accused stated at trial that he was just doing what everyone else was doing at the command -- stealing."

Voyles and one of his assistants, Christopher Angel, pleaded guilty at separate Navy courts-martial earlier this year. Voyles admitted taking $2,650 by filing phony vouchers; Angel confessed to stealing $1,435 the same way.

Voyles and Angel were reduced in grade to the lowest enlisted rank and given bad conduct discharges. Angel also was sentenced to three months in jail.

Last month, a federal grand jury in Alexandria last month indicted John B. Mason, a former member of the team, who is no longer in the Navy. Mason, 33, pleaded not guilty to the charges of filing fraudulent travel and training vouchers and stealing the underwater diving gear.

One Navy official familiar with the investigation said the inquiry has uncovered "a mixture of waste and pocketing money." He said the evidence showed that when the unit was set up in the early 1980s, "It did a lot of things wrong. Oversight mechanisms weren't in place. It didn't have the support on procurement. It wasted a lot of money."

A Navy spokesman said that special oversight and inspection programs for the unit are now in place.

Richard J. Marcinko, now a captain, was the first commander of Seal Team Six when it was set up late in 1980. In mid-1983 he was transferred to a special Navy unit at the Pentagon whose mission included security tests such as the one last year in California. He is one of several defendants in that suit.

Marcinko's attorney, John Perazich, said yesterday that he could not comment on the financial investigation because of a pending internal Navy inquiry. He said Marcinko's role in the California incident was only a supervisory one. "He didn't personally take part in any of the alleged personal injuries," Perazich added.

Several sources familiar with the inquiry said Marcinko, who has not been charged with any misconduct, is among those being investigated. They noted that he angered colleagues by raiding other Seal teams for their best men in the early 1980s to set up the special counterterrorism unit. His job as head of the mock terrorist unit penetrating base security also created hard feelings, they added.

The Naval Investigative Service (NIS), headed by Rear Adm. Cathal L. (Irish) Flynn, a former Seal, is partly responsible for the security of Navy bases. A Navy spokesman said that no one at NIS is "out to get" Marcinko.

Robert Eisen, a Norfolk lawyer representing Mason, the indicted former Seal, indicated at Mason's arraignment last month that his client's defense, in part, will be that it was team policy to disguise some expenditures to cover secret activities in procuring equipment for the unit's mission.

"The oversight, if any, was so sloppy that certainly Mason cannot and should not be held to account," Eisen said. "Responsibility for a policy that either didn't exist or wasn't enforced by any number of superior officers may run right up into the Pentagon."

For part of the period under investigation, Capt. R.A. Gormly was commander of Seal Team Six. Gormly now heads the navy's Special Warfare Group Two, at Little Creek, Va., which directs the activities of all East Coast Seal teams except Team Six. The counterterrorism Seal Team gets its orders from the Joint Special Operations Comand at Fort Bragg, N.C., the home of its Army counterpart, Delta Force. Gormly said yesterday that he had no comment on the investigation.

Voyles testified at his court-martial that when he arrived at Seal Team Six, "I knew right away there were some strange things going on. The funds there are virtually unlimited and the atmosphere is very lax and unregulated . . . ."

He said the man he was replacing showed him how to "make money" on travel claims, and that one lieutenant allowed "open book exams" for promotions and others authorized false bills at a sky-diving center. Voyles told the court that the investigation "is probably going to end up involving hundreds of people there."