A 23-year-old District man was gunned down in an ambush slaying last night when a group of men surrounded his car at a Southeast stoplight and fired point-blank with automatic weapons, D.C. police said.

The execution-style slaying occurred shortly after 7 p.m. at Southern Avenue and Chesapeake Street SE, an intersection crowded with evening traffic and pedestrians. Some onlookers said they dived to the ground as the gunmen fired into the car from several sides.

Witnesses said the car rolled about 20 yards backward from the corner as the assailants fled. Shell casings and glass littered the street, and most of the car's windows were shattered by bullets.

"I was standing on the other side of the street waiting for the light to change so I could walk, when all of a sudden I saw these flames or flashes from the guns," a bystander said. "I didn't know what happened, so I just hit the ground for cover. I looked up for a second and I saw all these guys running off. This is scary. Those bullets could've hit anybody."

The killing was the District's 44th in the first 39 days of 1988, twice the 22 slayings that had occurred by the same date last year. Police said that increasing drug- related violence and use of sophisticated weapons have produced the dramatic increase in homicides.

The victim, whom police identified as Bobby Parker of the 800 block of Chesapeake Street SE, was a drug dealer in the Washington Highlands neighborhood, where the killing occurred, sources said. Many of those watching police investigators said Chesapeake Street, lined with three-story brick apartment buildings and muddy alleys, becomes a bustling drug market each night.

Parker was taken to Greater Southeast Community Hospital and pronounced dead at 7:26 p.m. A hospital spokesman said an examination of the body showed 12 bullet holes, although the spokesman said some may have been exit wounds.

Detectives investigating the slaying last night struggled to gain the cooperation of bystanders pacing past the police tape around the car. "Everyone's getting amnesia real fast," one detective said. Some neighbors looked apprehensively over their shoulders before talking to police or reporters.

"I heard all these shots, like machine gun sounds," said one man, who declined to give his name. "I waited a bit, then went outside and saw the car roll back down the street, and I saw the guy driving slump his head."

Police said they believe that three or four men in their early twenties shot Parker, who was driving a recently purchased Toyota Corolla sedan. The assailants apparently sprinted toward the car as it waited at the stoplight, opened fire and raced about 50 yards down the street and through a small gravel parking lot next to an apartment complex.

Detectives said that they were uncertain of the type of the weapons used in the slaying and that they had not yet examined the inside of the car Parker was driving.

Police sources said that Parker was acquitted in January in connection with the Dec. 29, 1986, slaying of Korean store owner Byung Soo Pak. Pak, 62, was shot to death in his Capitol Hill market in the 100 block of Eighth street SE during a robbery attempt.

Pak was shot after a relative who was working in the store could not open a cash register. Police sources said Parker had been charged with first-degree murder and robbery in D.C. Superior Court.

Seventh District police said that they have made numerous drug arrests recently near the corner of Sixth and Chesapeake streets, which is about three blocks from where the shooting occurred. The area's drug trade has flourished lately, police said.

"There's a little bit of everything being sold there," said one detective. "It appears that's what the shooting stemmed from, but we don't know if the guy who was shot made a bad buy or was just set up to be ambushed."

Residents poured onto the streets in the minutes after the shooting. They said there have been several shootings in the neighborhood recently.

"When you hear shots, and you know they ain't shooting at you, most everybody around here comes out to look because they want to know who's being shot this time," one woman said as she stared at the bullet-sprayed car. "It's a real regular thing."