Adler Barrimore (Barry) Seal, the nation's top drug informer, worked as a Special Forces pilot in Vietnam and later flew for Trans World Airlines before he became a drug smuggler, earning $1.5 million for a single flight into Colombia and amassing a drug fortune of $60 million to $100 million.

But, according to officials of the Drug Enforcement Administration, after Seal was arrested three years ago, he began to walk an even more dangerous tightrope. He decided to become an undercover DEA informer.

Now, he's dead, and the DEA said he apparently was the first victim of a drug-financed Colombian hit squad whose sojourn into the country -- with botched getaways and flashy clothes -- might have been comical had it not been so deadly.

Seal, 45, became the key player in the government's top drug cases, DEA officials said. His testimony led to cocaine charges against a high-level Nicaraguan government official and drug convictions against the top government officials of the Turks and Caicos islands.

More recently, Seal had turned his attention to even bigger fish when he testified before a federal grand jury about three of his former employers: Colombian drug kingpins Carlos Lehder, Pablo Escobar and Jorge Ochoa. Lehder and Escobar are fugitives, and Ochoa is in prison in Spain, facing extradition to the United States.

Throughout most of his undercover career, Seal, a flamboyant man, lived with the knowledge that drug traffickers had placed a price on his head, but he refused government protection. He recently told television reporter John Camp in Baton Rouge, La., "I'm not worried about the contract. If it comes, it comes."

About six weeks ago, as part of his tangled plea-bargaining negotiations, Seal began serving a six-month sentence at the Salvation Army halfway house in his home town of Baton Rouge, leaving each morning at 8:30 for his job as a self-employed aviation consultant, and returning at 6 p.m.

Seal's new schedule did not go unnoticed.

Not long after Seal reported to the halfway house on Jan. 24, according to federal investigators, four Colombian men began a journey first to Panama, then into Mexico.

Officials of the Immigration and Naturalization Service said the men are believed to have illegally crossed the Mexican border into California Feb. 12.

DEA sources said the men bought new American clothing in an attempt to "blend in" as they made their way across the country. But it appears they should have had a fashion consultant on their shopping trip. By the time two of the men were apprehended, agents said one was wearing a "flashy" orange shirt with a brown suit and the other wore a pastel outfit that would have been appropriate on "Miami Vice."

About 6 p.m. on Feb. 19, as Seal pulled his white Cadillac Fleetwood into the Salvation Army parking lot, two men walked up to the car and began firing wildly with Ingram Mac-10 machine guns, small assassination weapons that fire at a rate of 1,000 rounds per minute. Seal died instantly.

Federal agents said that violence among Colombian drug dealers is common, especially in Miami. But they believe that the four Colombians who illegally entered the United States are part of the first "hit squad" sent here by drug traffickers to carry out a murder contract against a U.S. target. Security at DEA offices across the country was increased a year ago when Colombian traffickers let it be known that they had placed a price on the heads of top DEA officials.

Sources have said that the price on Seal was to have been $500,000 for his death or $1 million for getting him to Colombia alive.

Seal's family and some public officials have complained that Seal should have been better protected. Attorney General Edwin Meese III said last week that he is looking into how the case was handled.

But federal agents said Seal had refused offers for a new identity and that he rejected requests that he serve his six-month sentence in a halfway house in an area where he was not so well known.

Agents and others who knew Seal said that he was a self-styled soldier of fortune who became involved in drug smuggling for thrills. They said that Seal was an avid pilot who especially enjoyed pushing airplanes to their limits and modifying them with special equipment.

When Seal returned from Vietnam, he went to work as a pilot for TWA. But sources said Seal became bored with the routine and began to look for excitement.

Seal was arrested in 1972 for attempting to smuggle nearly seven tons of explosives to Cuba, but the case was later dismissed. He has said in interviews and in testimony to the President's Commission on Organized Crime that he got involved in drug trafficking by 1977.

He had appeared on numerous televised interviews and last year testified before the crime commission. Seal had bragged of once smuggling 20,000 pounds of cocaine into Baton Rouge without leaving his house, simply by ordering it by phone.

Seal lived in an upper-class neighborhood, surrounded by oriental rugs, jewelry, expensive art work, luxury cars, boats and airplanes.

Early last month the Internal Revenue Service seized Seal's house, two boats, several planes, real estate and other possessions for alleged nonpayment of $29,437,718 in taxes on illegal drug income.

Camp, an investigative reporter for KBRZ-TV in Baton Rouge, said that Seal underwent a "personality change" when he went to work for DEA and became serious about working against his former employers. Agents familiar with Seal's work said he was extremely valuable to the DEA, with a memory for details that was close to photographic.

Although Seal will not be able to carry out his planned role as the government's star witness in the Ochoa trial, federal sources said Seal's testimony to a grand jury may still be able to convict his old associate.

After the killing, a major federal manhunt was launched. So far, six men have been arrested in connection with the killing. They are being held without bail on a variety of charges while the investigation continues.

Within 12 hours of the shooting, three of the suspects were arrested. They included Miguel Velez, Heriberto Sanchez-Cardenas and Jose Renteria-Campos.

One of the men was arrested in New Orleans, a second at the Miami airport and the third was arrested after the taxi he had hired to drive him from New Orleans to the Montgomery, Ala., airport hit a deer in Meridian, Miss., and became disabled.

A federal official said the other two suspects had raised suspicions among personnel at the New Orleans airport as they ran through the terminal offering large sums of money for any flight that would take them to Miami.

Federal sources said that Sanchez-Cardenas and Velez are believed to be among the Colombians who illegally crossed the border Feb. 12. Renteria-Campos, a Colombian, was already in the United States on an expired visitor visa, the sources said.

Two days later three other men were arrested by the FBI in simultaneous raids in the New Orleans area. They included John Jairo Cardona-Garcia, Luis Carlos Quintero-Cruz and Bernardo Antonio Vasquez-Tamayo. The FBI announced that agents found drugs and weapons during the raids.

INS officials said that the first two men are believed to have crossed the border illegally Feb. 12, while Vasquez-Tamayo, a Colombian, is a permanent resident alien living in New Orleans.

FBI spokesmen in Louisiana said that all the men were being held in connection with the Seal murder while the investigation continues.

By the end of last week, Velez had been charged with retaliation against a federal witness, conspiracy and obstruction of justice. Vasquez-Tamayo had been charged with conspiracy, obstruction of justice and a firearms violation. The other four men were being held as illegal immigrants.