Lawrence Marsolais, a former employe of a downtown Washington restaurant, was walking along Columbia Road on a recent Sunday when someone stopped him and said, "Hello, amigo!"

Marsolais was startled to see a 33-year-old illegal alien from El Salvador who had worked in the restaurant until last year.

"I couldn't believe it," said Marsolais. "This guy had committed a crime and was deported. Now he's back and just walking around as if nothing happened."

Each year, perhaps as many as 200 illegal aliens, arrested on criminal charges by local police, are turned over the the Washington office of the Immigration and Naturalization Service for deportation. Unlike the Salvadoran, many are never tried, a senior immigration investigator in Washington says, because it takes too much time and money.

"Most of them [judges, prosecutors and police] will do it like that," he said. "They say, 'Why should we burden the taxpayer when we can pass them on to the Immigration Service'."

But, like Marsolais' former coworker, an estimated 80 percent of the aliens who are deported turn around and come right back, often slipping across poorly guarded borders during the night.

"We see a lot of [individuals who have been charged criminally and deported] that just keep coming back and coming back," said Michael G. Harpold, an immigration agent and president of the union that represents Immigration Service employes.

When illegal aliens like the Salvadoran turn up again, the INS says there is little it can do, particularly at a time when its staff has been cut back and it is overwhelmed with problems like the recent influx of Cuban and Haitian refugees.

When Marsolais called to say he had seen his former coworkers, he was told that the local INS office had no one available to go out and search for him. t"Look, and even if we did, we don't know where the guy lives or works," a staff member explained to a reporter. "He won't have a phone number and he's probably changed his name. Now, how can anyone find someone like that?"

While neither the INS nor any area police department keeps statistics on the number of illegal aliens arrested or the disposition of their cases, immigration officials say that they receive at least one call each working day from courts, jails or police to come pick up an illegal alien for deportation.

The number of crimes committed by illegal aliens is probably higher than that figure reflects, because many of the crimes are committed against other illegal aliens, who often are reluctant to report the incident for fear it would jeopardize their own situation.

The worker Marsolais recognized, for instance, had been arrested for stabbing another illegal. An investigation occurred only because the victim had needed to be treated for a wound. Otherwise, officials say, it is unlikely the crime would have ever found its way onto the police blotter.

Local jurisdictions have differing policies on how the cases of illegal aliens arrested on criminal charges are handled.

D.C. police policy is not to turn over illegals to the Immigration Service, but rather to leave the decision up to the prosecuting attorney, a spokesman said. But one senior INS investigator here said that his office gets a number of calls each month from the D.C. police or jailers who prefer to hand illegal aliens over rather than process them.

The U.S. Attorney's office here says its policy is to prosecute illegal aliens and then decide whether to sentence or deport them, in consultation with the presiding judge.

Officials in most suburban jurisdictions said they were not sure what the policy was on illegal aliens who had been arrested in that county are turned over to the Immigration Service for deportation proceedngs and charges are then dropped.

According to the defense attorney who represented the Salvadoran, the disposition of that case was typical. "He agreed to plead guilty to a reduced charge of carrying a weapon rather than assault with a weapon," said the attorney. "We [the judge, U.S. attorney, and herself] got together and agreed that the best way to handle it was to simply give him credit for time served [about a month] and have him deported. It was reduced to a misdemeanor from a felony, so it will have less impact on him.

"It was a good way to pass the buck," she said.