The reign of underworld chief Carmine (Lido) Galante ended this afternoon in the cramped garden of a small Brooklyn restaurant as he and two other men were shot to death while eating lunch.

According to police, three men wearing ski masks entered the Joe & Mary Italian-American Restaurant in the Bushwick section of Brooklyn at 2:45 p.m., passed quickly through a nearly deserted front room and out into the small garden area, where they emptied two automatic weapons and a shotgun into Galante and two others at close range.

Killed with Galante, 69, were his chauffeur-bodyguard, Leonardo Coppola, 40, and the restauranths owner. Giuseppe Turano, 48. Turano's 17-year-old son, John, was shot and is listed in critical condition at a nearby hospital.

A fourth person at the luncheon table, who was not immediately identified, apparently escaped injury.

A police spokesman said the gathering was apparently a bon voyage party for Turano, who was to leave this weekend to join his wife and daughter on a European vacation.

Galante, still with a cigar in his mouth, and Coppola died "very rapid deaths," according to New York City chief medical examiner Michael Baden. Turano died at a hospital later.

Police had no idea who was responsible for the killings, but, as one detective said as he came out of the restaurant tonight, "It's inevitable with these guys. Very few of them die in bed."

According to Deputy Police Inspector Martin Hayes, the killer "were executioners, it's that simple."

The slaying was the most dramatic underworld assassination since Joey (Crazy Joe) Gallo was shot to death on April 10, 1972, in Manhattan's little Italy while dining out several hours after his wedding.

"This is the biggest thing to hit this town in quite a while," one policeman said as he waited with an army of reporters and others for the bodies to be removed.

Hundreds of police combed Brooklyn, blocking roads, rerouting traffic and asking questions.

By early evening, a few hundred people were shoulder to shoulder along police cordons barring entrance to the small storefront restaurant with a sign over the door that reads "special attention to outgoing orders."

Reporters were everywhere, devouring one rumor after another. Television lights atop cars and vans added to the feeling that this was something far above the usual brand of homicide in this city.

Shortly before 7 p.m., police carried the bodies of Galante and Coppola, wrapped in rubber bags, to a waiting mortuary division van. Baden, accompanied by two associates, appeared later to tell reporters that the two had died of "multiple gunshot wounds." He did not elaborate.

"I heard a lot of shots," said the proprietor of a business down the street from the restaurant. "I thought it was some firecrackers. When I saw a guy with a rifle, all I did was come back in my store. I didn't want to get shot."

Police said six gunmen, all wearing ski masks, took part in the assault. Four of them arrived at 2:45 p.m. in a blue Mercury, they said, and three went in while the fourth kept watch outside, keeping passersby at bay by sweeping his shotgun toward any who came near.

Meanwhile, they said, a second car pulled up, and two gunmen walked into the restaurant, shooting young Turano, who was talking on a pay telephone. They ignored three diners and left.

Witnesses said the drama was over in less than five minutes.

Galante had dismissed reports by authorities that a contract was put out on him while he was in federal prison in Danbury, Conn., last fall.

Galante, a stocky, bald man often seen jogging along the East River in the early mornings, was far more than the dry cleaning proprietor in Little Italy he claimed to be.

Galante was reported to be head of the 200-member Mafia family once run by Joseph Bonanno. He had been depicted in New York publications as a leading candidate for the "boss of bosses" mantle of the late Carlo (Don Carlo) Gambino.

He was involved in crime at the age of 10 and, according to authorities, never stopped. Born in east Harlem on Feb. 21, 1910, he served time in prison for narcotics violations and attempted armed robbery.

He also had faced charges of assault, bootlegging, extortion, gambling and homicide in the death of a New York City policeman in 1930.

At the time he was shot, Galante was free on $50,000 bail after his constitutional rights were adjudged violated during hearings which led to his imprisonment in 1977 as a parole violator. The U.S. parole commissioner reportedly voted last month to return Galante to prison.

But he was said to be entitled to a federal court hearing before he could again be incarcerated. CAPTION: Picture 1, In N.Y. restaurant garden, police detective starts to cover slain Galante, cigar still in his mouth. UPI; Picture 2, New York police remove Galante's body from Brooklyn cafe where he was shot. AP