When Juan Flores arrived at his Arlington construction job last week, he was still mulling over the news that a friend back home in El Salvador had been killed in the violence there.

As Flores walked through the entrance to the construction site, a tap on the shoulder jolted him back to reality. It was an agent from the Immigration and Naturalization Service, and the illegal alien knew immediately that his year-and-a-half stay here was over.

Yesterday Flores and seven other Salvadorans, caught in the same INS action last week, glumly watched the final processing of their deportation orders. By noon today, they will be on a plane going home, to a country where 800 people have died in political violence this year.

Unfortunately for those eight and 18 others apprehended, including nine more from El Salvador whose deportation hearings have yet to be held, Thursday's INS stakeout was the last the local INS office said it will undertake until July 1.

The Justice Department has ordered the INS to stop such "area control operations -- in which places frequented by undocumented foreigners are put under surveillance -- for three months. The halt was called so that illegal aliens in this country would not feel threatened by the taking of the census, which is now under way.

By calling off the raids, the government hopes to encourage more of the aliens to participate in the census. Specific census reports are confidential and not distributed to other federal agencies such as the INS.

As the INS was making its arrests Thursday, the capital of El Salvador was preparing for the funeral services of assassinated Catholic Archbishop Oscar A. Romero. Three days later, a riot at the funeral left 30 dead, most of them crushed when thousands panicked at the sound of bombs and gunfire.

It is that violence that is prompting several groups and individuals to argue that the State Department should allow Flores and other Salvadorans to remain here.

"In effect, the State Department is sending these people home to their deaths," said Michael Maggio, an immigration attorney. Salvadorans make up 65 percent of the clients of Maggio's law firm.

"We don't blame the INS. They're just doing their job. It's the State Department that's responsible," he said. He added that the department allows Nicaraguans who are here illegally to remain until the political situation in Nicaragua stabilizes, and should institute a similar policy for El Salvadoreans.

Maggio's view was echoed by Sharon Armuelles, director of Ayuda, an organization here that helps Latinos with immigration and other problems. She said that the city's coalition of Hispanic self-help groups met yesterday to discuss the arrests and imminent deportations.

"The Consejo [the Hispanic umbrella organization] feels very strongly that the political situation in the country would warrant us asking the State Department . . . to allow extended voluntary departure time for those apprehended," she said. "During this time, they should be allowed to continue to work."

According to Armuelles, the INS arrests were triggered by a telephone call from a "disgruntled American worker who couldn't get work [at the particular job site]."

INS officials refused to comment on what prompted them to stake out the project at Wakefield Road and Walter Reed Drive in South Arlington.

INS Director Kellogg Whittick said that two of the half-dozen INS agents who handled the stakeout were injured. One received scrapes when he was struck by a car driven by an alien trying to flee. A second agent severely sprained his ankle chasing an alien.

"You don't always like how you get the information," Whittick said in discussing the huge numbers of anonymous tips that often provide leads in INS investigations. "Some of them are from unhappy workers, some from angry girl friends. But that's what we have to rely on sometimes."

Flores' capture -- about two weeks after he failed to appear for a hearing after an earlier INS arrest -- was a bitter pill for the 20-year-old to swallow.

"I was earning about $200 a week," he said. "I sent $100 a month home to my parents."

Now, he said, he will be an unhappy surprise for his farmer father when he arrives at home. "They do not know I am coming," he said. "They did not want me to come back because of all the problems."