Thomas Norman Bracken was buried today in San Salvador's La Bermeja Cemetery. No mourners attended the funeral. His estranged wife in the United States sent a money order to cover what she specified should be the cheapest interment available.

The simple ceremony drew an end to one man's unhappy involvement in the increasingly violent struggle for El Salvador. No one seems to know how his role in the shadows began here. But now everyone knows how it ended -- bullets in the head and chest that felled him on the street of a San Salvador suburb last night 4 1/2 years after he left a comfortable job as police sergeant in North Las Vegas, Nev.

Bracken, the fifth U.S. citizen to be killed in El Salvador in less than two weeks, was in this country to help the National Police fight what they consider foreign-inspired communism aimed at El Salvador's peasants. His job reportedly was to advise on investigation techniques, but the mark he left on his students and their cause does not seem to have been deep.

"It is curious that your American papers should be so interested in someone who was so . . . let us say . . . insignificant," said a National Police official asked about the American.

A thick-set, balding man with large jowls and small eyes, Bracken, 46, was perhaps an example of the wanderers passing through the convulsed Central American region looking for work with guns. He often was seen at the bar of the Camino Real Hotel looking for someone to talk to. Frequently several expatriates -- American, Cuban or Nicaraguan, or, on occasion, Belgian -- are exchanging war stories and regretting what they see as communist infiltration.

Ironically, Bracken was considering a return home just before he was killed. On Dec. 11, a U.S. Embassy spokesman said, he walked into the consular section to ask about going back to the United States.

There was a problem, however, a U.S. federal warrant for his arrest issued in El Paso, Tex., on March 25, 1980. The warrant, sought by the U.S. Treasury's Bureau of Alcohol, Tobacco and Firearms, charged Bracken with transporting 19 .357 magnum pistols, a .38 derringer, an M1 rifle, four 12-gauge shotguns, 18 tear-gas grenades, 30 cans of chemical repellent, some .357 magnum casings and a vial of morphine from Las Vegas through El Paso into Mexico.

Hardly had Bracken crossed the border at Ciudad Juarez on July 3, 1979 -- when Mexican customs police said they found the arms stashed in the door panels and under the floorboards of his Nevada-registered Ford. Accounts differ about how Bracken got out of Mexico -- Mexican officials say he bolted to freedom and sneaked back across the river into Texas but some sources suggest money changed hands.

In any case, Bracken continued the security-consultant contract work in El Salvador that he had started after leaving the North Las Vegas police force as a sergeant July 30, 1976, for what one of his colleagues said he described as "a good opportunity."

The work, of course, took Bracken to El Salvador, where private companies sought extra protection against the violence pitting leftist guerrillas against police and, on occasion, rightist killer squads. A national Police official said he was hired officially last January to teach what he kenw about investigation and arrests.

According to the most reliable of many confused versions of his death, Bracken was killed in an accidental shootout with the personal bodyguards of Antonio Morales Erlich, one of four members of the ruling government junta. The bodyguards had nothing against Bracken, officials said. -- they were just driving by when a gunfight erupted. They joined it, and they shot Bracken "under accidental circumstances."

Officially, there is little known about what happened or why, or even to whom. The U.S. Embassy says Bracken was employed by the National Police. The National Police spokesman answers all questions on the subject with "no comment." He was surprised to learn that the information office of the armed forces issued a statement last night confirming Bracken's death and the fact that he was in the employ of the National Police.

The armed forces' statement says Bracken was with a guard of police investigating a kidnaping case when he went into a house where a wounded guerrilla shot and killed him.

Another version of events hinted at by the local press and endorsed and expanded by a high-level officer in the security forces, is that Bracken and another man were driving to a street leading up to the trouble-plagued village of San Antonio Abad on the outskirts of San Salvador. Bracken got out of his car to check a parked automobile that had blood stains on it when shooting broke out farther up the hill. At precisely that moment Morales Erlich's four-wheel-drive station wagon drove around a corner and down the hill toward where Bracken was standing. According to this account, Bracken pulled out a .38 revolver and ran into the street, attempting to stop the junta member's armor-plated vehicle, but the bodyguards inside fired and killed him.