A U.S. Park Police patrolman was shot three times and critically wounded yesterday in an exchange of gunfire with a motorist he pulled over for an apparent traffic violation on the Baltimore-Washington Parkway, authorities said.

Police still were searching last night for the man who shot Officer K. David Wallace in the neck, stomach and leg and then sped away, abandoning his car just inside the District of Columbia on Bladensburg Road. Officers said they believe the same man held up a couple one hour later inside a mausoleum at Fort Lincoln Cemetery and stole their 1971 Pontiac LeMans. That car was found yet another hour later abandoned outside a bar in Riverdale.

"It just goes to show you there's no such thing as a routine traffic stop," one of Wallace's colleagues said sadly yesterday as family and friends of the wounded 36-year-old officer gathered outside the emergency room at Prince George's General Hospital while he underwent five hours of surgery.

Park Police said Wallace stopped a motorist -- a man witnesses described to police as having long, sandy-brown hair and a "protruding pot belly" -- early yesterday just north of the New York Avenue exit of the parkway. Minutes later, police said, Wallace radioed for help.

"He sounded really bad," said a Park Police officer who heard the call. "His voice was like weak. He sounded like he was really hurting."

Police said Wallace had obtained from the motorist a driver's license and car registration papers bearing the name of Billy D. Hindman, 31, of Nashville, Tenn., and was walking back to his cruiser when the shooting allegedly began. Wallace returned fire and struck his assailant's Datsun 280-Z as he drove away, police said.

When other policemen arrived minutes later, they found Wallace lying beside his car, Hindman's drivers' license and registration papers underneath him, officers told Wallace's family. Wallace's service revolver lay empty inside his police cruiser, one officer said.

In the minutes following the incident, police began zigzagging between Maryland and D. C., trying to pick up the trail of the gunman. After speeding away from the 8:43 a.m. shooting, the suspect abandoned his car in the residents' parking lot of a Bladensburg Road high rise, police said. One hour later, at nearby Fort Lincoln Cemetery, a couple visiting a gravesite was held up at gunpoint by a man matching the motorist's description, officers said. The man sped away in the couple's 1971 Pontiac, according to Park Police.

Riverdale police officers found that car later in the morning, parked outside Heinecke's, a restaurant and bar on Rhode Island Avenue, prompting an extensive manhunt throughout the area. "They even came in here and looked in our refrigerators, they looked everywhere," said the manager of Heinecke's, who refused to give his name.

Police dogs apparently followed the fleeing man's scent to a spot near Leland Memorial Hospital in Riverdale, but lost it after a heavy downpour began in the early afternoon, officers said. The search had shifted to Cottage City near the District of Columbia line by nightfall.

The shooting was the first of a U. S. Park police officer here since May 1975 when two officers were seriously wounded during a gun battle with a homicide suspect at the Jefferson Memorial.

For Wallace's family and friends, the day was filled with painful ironies. The shooting occurred about five miles from a spot on the same highway where nine months earlier Wallace had delivered a baby boy -- an act that earned him a commendation from the Park Police.

Also, Wallace had rarely gone out on duty without wearing his bulletproof vest -- until yesterday, according to his brother, Andy. "It's the first thing everybody thought," said Andy Wallace. "I don't know why he didn't have it on. Maybe he figured it was Sunday, it was raining and he thought it would be an easy day."

Andy Wallace leaned against a wall outside the emergency room and recalled how his brother had delivered the baby of Vineta Faison, who had gone into labor on the Baltimore-Washington Parkway last February as her parents and husband drove her to the hospital. Faison's father flagged down Wallace, who stopped to help out, and ended up delivering a 5-pound, 12-ounce baby boy in the car.

"That's mostly what he did. He assisted motorists and worked traffic," Andy Wallace said. He pulled a snapshot of himself and his brother from his pocket, and said of the wounded officer, "He's the clean-cut one." He pointed to a stocky, dark-haired man who was smiling broadly in the photo. Secluded in a family waiting room, Wallace's wife and two children waited for reports of his condition.

Wallace was in critical but stable condition in the intensive care unit after surgery on his neck and stomach, according to an emergency room nurse. The neck wound was the most serious, relatives said, adding that doctors will not know for two days whether Wallace will be paralyzed as a result of his wounds.

David Wallace joined the Park Police about 10 years ago, his brother said, and saw it as a step up from his earlier job as a D.C. patrolman. "He was dedicated," Andy Wallace said. "I can't say he loved it, but he tried to do his job."

Moments later, a Park Police official who joined the vigil walked up to Andy Wallace, clasped his hand and said sadly: "I'm very sorry. As you know, he's a police officer. This is part of our job."