Linwood Gray, a muscular, 33-year-old Southeast Washington man who once beat up a Probation officer in court, told a judge he was Al Capone reincarnated and spent six years in a mental hospital, is now believed by law enforcement officials to be the head of the largest, most successful narcotics operation ever discovered in this city, sources said.

The alleged Gray ring is believed to be connected to a number of people in other smuggling operations, yet it is unusually well-knit and dfficult to penetrate, the sources said. It has been able to smuggle heroin from the opium fields of Southeast Asia through capitals of Western Europe into major cities of this country and on to the District of Columbia, sources said.

There is "a steady good supply" of drugs, said one law enforcement source familiar with the operation. Investigators believe they have traced about 200 pounds of high quality heroin to the ring, far more than has ever been linked to any other smuggling operation here.

Gray and a couple of dozen of his alleged operatives are the targets of a year-long investigation by police and federal agents here. Evidence was being presented to a grand jury, with the investigation reportedly drawing to a close, when the leader fo the probe, Assistant U.S. Attorney Barry L. Leibowitz, was shot and slightly wounded in front of the U.S. District Courthouse here Wednesday.

Officials investigating the shooting believe that the gunman, who escaped, was trying to intimidate would-be witnesses.

Leibowitz, shot once with a silencer-equipped 22 caliber pistol, suffered only a flesh wound when he turned abruptly from the gunman. He was back at work Friday and the task force of metropolitan police and Drug Enforcement Agency agents was moving ahead with its case. Some of these investigators were initially fearful that the shooting of Leibowitz and publicity surrounding it would casue witnesses, informants and ring operatives to disappear. The Post learned and published that two people connected to the ring-one in Amsterdam, Holland, and one in New York City-had been murdered previously. Some homicide detectives here also suspect that the ring is involved in at least two other recent drug-related murders here.

However, investigators have yet to link any of these deaths or the attempted murder of Leibowitz to the investigation of the alleged Gray operation.

In the meantime, background on Gray and his alleged ring hav eemerged from court papers, police sources, and a number of sources with knowledge of the drug investigation.

Gray grew up in the Garfield Heights section of Southeast Washington. Several policemen and former policemen remember him as a braggart and particularly nasty. "He was a plice fighter-he just loved to fight policemen," said one, noting that because of Gray's size, a number of officers were usually called to the scene of any disturbance involving him. At one arrest in the 1960s, Gray stood 6 feet 1 and weighed 260 pounds "and not an ounce of it was fat" said one former policemen.

"He told me that no one would ever arrest him twice and if he saw me again he would blow my head off," said the former policemen.

In a courtroom appearance in 1967, Gray beat a probation officer about the head and shoulders with both fists and had to be restrained by four court officers, according to news stories published at the time.

Gray was charged with bank robbery in Maryland in the 1960s and later convicted and was charged in the District in 1967 with carrying a dangerous weapon.

At his trial in the District, he said he heard voices advising him that he was the reincarnation of A1 Capone and a judge ruled him not competent to stand trial.

He spent seven years in St. Elizabeths despite repeated attempts by defense attorneys to get him out, and ultimately was released conditionally it, 1974 and permanently in 1976.

The alleged Gray organization began to come under intense law enforcement scrutiny about a year ago, with prosecutors, federal agents and police joining forces to identify and crack entire drug smuggling organizations, rather than the simple street peddler.

A main break in the investigation occured last February when a South-east Washington resident, George Franklin Carter, was arrested at O'Hare International Airport in Chicago as he tried to smuggle over two pounds of heroin into the country in cigarette packs, sources said.

Carter was a Vietnam veteran with no previous criminal record but investigators here have described him as an operative in the alleged Gray organization.

Carter was arriving on a flight from Amsterdam, whihc investigators say is a key transit point for heroin into this country. They say the alleged Gray organization couriers frequently try to conceal drugs in cigarettes.

In May a federal court judge in Chicago sentenced Carter to 12 years in prison after Leibowitz and an assistant U.S. attorney in Illinois told the judge Carter had no remorse and refused to cooperate with prosecutors.

Porsecutors at Carter's sentencing also portrayed him a splaying "a significant part" in "a major narcotics organization" that "travels the world over spending considerable sums of money purchasing high quality narcotics on the world markets." This organization, according to the prosecutors' statement "goes to great lengths to hide itself from detection using such devices as false passports and duplicate passports."

In their statement, prosecutors linked Carter to Ernest Henry Minder, another Southeast Washington resident, who prosecutors said had been a drug-dealing associate of Warren Christopher Robinson.

Robinson was a major drug trafficker in the District and investigators have said he purchased drugs both from Mafia figures in New York and later through a network of servicemen and ex-servicemen in Southeast Asia and Germany.

Robinson was sentenced to 16 years in prison in 1975 for narcotics violaition charges. Minder was found shot to death on Oct. 2 in his luxury car in the 2500 block of Naylor Road SE. Police have no suspects, but are investigating the possibility that the death was connected to the alleged Gray ring.