Law enforcement authorities have issued a warrant for the arrest of a 28-year-old Northwest Washington man, Robert Earl Lyons, charging that he was the triggerman in the shooting last month of a federal prosecutor here who was investigating a major heroin ring.

Lyons is charged in the warrant with conspiracy to murder in connection with the shooting and wounding of Assistant U.S. Attorney Barry L. Leibowitz. An affidavit filed with the warrant said Leibowitz had selected Lyons' picture from several different photographs and had positively identified Lyons as the man who tried to kill him.

Leibowitz was walking into the U.S. District Courthouse here on Dec. 20 when he was shot at point-blank range by one of two men in a passing car. One shot struck him above the right hip as he turned suddenly, and the car sped away. Leibowitz was hospitalized for a day, then released. He has since been living under 24-hour guard by

Lawmen have pursued the shooting on the assumption that it was an attempted contract killing. They are still attempting to determine if the shooting is connected to Leibowitz's investigation of the drug ring, according to informed sources.

In an interivew with The Washington Post yesterday Lyons' father, Lorenzo Lyons, said he believed "it is just about impossible" that his son would have shot at Leibowitz. "He's a normal boy," the elder Lyons said.

Lorenzo Lyons, a 51-year old construction worker, said Robert is one of nine children in a family that grew up in the District of Columbia. He said he believed his son attended Dunbar High School, but he was not entirely clear about what has happened to him since.

"I just try to get them (the children) on their feet," he said. "I can't follow them everywhere."

The elder Lyons said Robert "had got into some trouble" in New York state when "he went there with some other boys," and had served some time in the state correctional facility at Attica. He also attended school near Buffalo, he said.

Lyons said that while his son was in prison doctors found that he had cancer and was only given a few years to live. He said his son was depressed about that, but "kept it to himself -- he never sang out about anything." He said that he has not seen his son since he left after a brief visit four months ago, and does not know where he is.

Leibowitz got an excellent view of his attacker, according to the affidavit and informed law enforcement sources was recounted the incident.

As he crossed C Street en route to the courthouse, Leibowitz looked to his right and saw a small car, double-parked and facing 3rd Street NW, according to the affidavit.

At the same time Leibowitz "saw a full-sized, light-colored car, which had also been double-parked but to the rear of the smaller double-parked car, proceed toward 3rd Street and pull alongside the smaller car," the affidavit said. Then Leibowitz saw a passenger in the large car appear to have a conversation with a person in the smaller car.

As Leibowitz entered the parking area on the 3rd Street side of the courthouse, "the full-sized, light-colored car pulled into the parking lot behind him and approached him from the rear," the affidavit said.

Someone in the car called his name and Leibowitz leaned over and saw at least two men in the car, the affidavit said. At that instant, according to informed sources, Leibowitz found himself two feet from a man in the passenger side of the car who was pointing a silencer-equipped,.22-caliber pistol at him. Leibowitz momentarily thought that it was some kind of flare gun, the sources said.

While about 25 lawmen from four different agencies combed

The first shot tore his necktie from his neck and the second, fired while the car was moving away, struck him.

While about 25 lawmen from four different agencies combed the area for the attackers, the two men apparently drove three blocks away to Hecht's garage at 6th and E streets NW, parked the car, and left, according to law enforcement sources.

On Dec. 29, an attendant at Hecht's notified police that a car was afire there. Police searched the burned out, silver, 1973 Pontiac Bonneville, and found a shell casing that matched one found on the driveway ramp where Leibowitz was shot.

Investigators theorized that the suspects returned to where they had parked the car and set it afire to eliminate possible fingerprints. But shell casings are ejected so fast that in moments of haste it is not always possible to tell where they have fallen.

Police homicide investigators McKinley Williams and Larry Williams traced the car to a metropolitan dealership, where it was purchased for about $800 cash, sources said.

While police looked into this and several recent drug-related deaths, information they developed led them to run a check on Lyons, sources said. A computer revealed that he was sentenced to prison in New York for manslaughter and robbery, and was wanted in that state for parole violation, according to the sources

The picture of Lyons, transmitted by New York authorities, bore a striking resemblance to a composite put together by a police artist working from Leibowitz' recollections, sources said. FBI special agent Urey Patrick, working with the Williamses, arranged the photo spread shown to Leibowitz.

The FBI obtained an arrest warrant about two weeks ago, but kept it sealed at U.S. District Court for fear Lyons could flee or be killed if it was known that he was wanted.

Lyons, nicknamed Drops, was believed sighted in the area several times over the next few days, but police could not locate him and now concede they do not know where he is, according to law enforcement sources.

With knowledge of their search well known on th streets, police issued at the end of the week a teletype lookout for Lyons to law enforcement agencies in other cities.

Police are also attempting to determine whether the attack on Leibowitz is connected to the deaths of Raymond Lee Adams and his girlfriend, Nancy R. Gilmore, Dec. 12.

The body of Adams, 52, was found in a Cadillac registered to Gilmore and parked in the 6600 block of 13th Street NW. He had been shot twice in the head. Nine hours later police found Gilmore strangled in her home at 6630 Georgia Ave. NW. Medical examiners said both had died about 1 a.m.

Adams was on parole after serving a prison sentence for a drug conviction. Police are operating on the theory that the deaths were drug-related.

Law enforcement authorities believe the heroin ring that Leibowitz was probing is the largest ever discovered in the District of Columbia. Those authorities believe that the ring is unusually well knit, and has been able to consistently smuggle heroin from the opium fields of Southeast Asia through Western European capitals, principally Amsterdam, and into this country.

The Washington Post reported on Dec. 24 that the federal investigation of the drug ring has targeted Linwood Gray, a 33-year-old Southeast Washington man as head of the operation.