For three years Lydia Jackson worked nights cleaning offices and lounges at Washington National Airport. Then in June the janitorial company that employed her and 16 other union workers lost its contract. They all lost their jobs.

The new cleaning company's crew is non-union and comprises in large part refugees from Vietnam and Cambodia.

"Blacks are taking the bad enough jobs as it is now, but now they cannot even count on jobs in cleaning," says Jackson, 41.

To Pat McDonough, an organizer for local 82 of the Service Employees International Union, which represented the laid-off workers, what happened was simple. "It's a concrete situation where American workers are being displaced," he says. "They the employers get a more docile work force and don't have to pay the minimum wage."

Historically the nation's capital has not been a major entry point for immigrants, who preferred to go to more industrial cities where opportunities for unskilled labor were more plentiful. But in the past decade an influx of immigrants from Asia and Latin America has made Washington a melting pot, with one recent study estimating that as many as 250,000 persons--one out of every 12--is foreign-born.

Some labor officials and black leaders cite what happened at National as a foreshadowing of what that influx could mean in the years to come.

The new immigrants are getting jobs as dishwashers, hotel housekeepers, food servicers, drycleaners and construction laborers. While they have not had the same impact as in states like Texas, California and Florida, the worry is real that they could end up with jobs that once went to blacks or to union labor.

"There is some concern among workers in our community, many of whom are black . . . that jobs traditionally held by blacks are now being held by members of other minority groups," says City Council member Charlene Drew Jarvis. "It is a broad group--Orientals, Hispanics, East Indians--and among many blacks there is grave concern at what they perceive as displacement."

Marchel Smiley, president of local 722 of the Service Employees union, whose 1,800 members work in two District hospitals and seven outpatient dialysis clinics, says low-paying jobs in the health area, like housekeeping and laundry, are increasingly occupied by immigrants.

"There were no whites, traditionally, because they've been the most undesirable jobs. But starting basically with the Vietnam situation and with some other situations now we're seeing more and more Orientals and Asiatic-type employes," says Smiley.

In a study last March for the Greater Washington Research Council, demographers Eunice and George Grier noted that tensions between the newcomers and the broader community exist "below the surface" partly "because people in the established community--especially black Americans--fear that the newcomers may take jobs and housing away from them."

"It's more of a concern within individual locals, but labor as an institution has not addressed the problem as a priority," says Smiley, in a remark repeated by other union leaders.

Though some jobs such as dishwashing and domestic service are being filled by immigrants because they are jobs many Americans shun, that is not always the case. And the situation at National is a case study of the kinds of issues raised when both seek the same job.

During the past year, three airlines--Piedmont, TWA and Eastern--switched the contract for cleaning their facilites at the airport from Allied Maintenance Corp., a New York-based national building service company, to a small, local firm called Clean Aircraft, whose non-union work force is predominantly Vietnamese and Cambodian.

Spokesmen for the airlines indicated that both economic reasons and dissatisfaction with Allied's services were factors in their decisions to change--which took place after competitive bidding.

As a result of the three transfers to a non-union contractor, at least 50 people have lost their jobs. Although they applied for work at Clean Aircraft, they were not hired, McDonough says.

Philip Stout, owner and manager of Clean Aircraft, says he received four applications from former Allied workers and that he sent each one notification by phone or mail that there were no positions available at the time.

"As a policy I do not hire from a contract that I am replacing. I would rather get new people," Stout says.

Stout says he pays new workers $3.70 an hour, and after a probationary period of 90 days they get a 15-cent-per-hour raise, with guaranteed raises every year. The union's starting hourly wages are between $3.83 and $4.45, McDonough says.

Stout says he does not offer the medical benefits that Allied gave its unionized workers because the costs for a small firm like his are "prohibitive."

When he started Clean Aircraft his work force was predominantly black, but on the recommendation of a friend he hired two Vietnamese workers, a 56-year-old man and an 18-year-old woman.

One day, a half hour before a shift was to start, he found out the man wouldn't be coming to work because he needed an operation. "Mr. Cheng showed up and said, 'I'm going to work for my friend until he comes back so he won't lose his job.'

"Never in all my years of business had that happened to me," says Stout. "I hired him on the spot." Eventually he made Philip Cheng his supervisor. Today his 42 workers include Vietnamese, Cambodians, Afghans and Ethiopians, he says.

Stout, a 31-year-old Fairfax resident who believes in the "American work ethic," heaps praise on his workers. "They all smile; they take directions easily; they are prompt to meetings," he says.

Stout's experiences with the new immigrants is a common one, according to Elaine Squeri, a job developer with the Refugee Education and Employment Program in Arlington.

"The refugees come from a traumatic background. They have a lot of desire and zip to work," she says. "Some employers are impressed with that willingess that is unlike American workers. What I hear is that American workers--not just blacks or not just whites--have lost the idea of what it means to work a full day and start at the bottom. They're not very exciting jobs: porters, emptying the trash and sweeping hallways. But for refugees it's a whole new life."

For Cheng, who had to leave his wife behind in Vietnam, the job is a new lease on life. The 54-year-old Chinese, who speaks six languages and worked as an office manager for a U.S. company in Saigon for 10 years, says: "First thing, I like to stay in this country. I lost everything. I'm working very hard."

Sometimes the newcomers offer advantages to employers that American workers are unable to match and, indeed, find strange. "When they are sick they send in someone to work for them," says local 82 shop steward Christena Greene. "Americans cannot do that. If I'm off sick, I cannot send in my sister in my place to work because they will want to know why I do this."

Some local unions have aggressively sought membership from new immigrants. Local 25 of the Hotel and Restaurant Employees, for example, reports that 20 percent of its membership is Hispanic, and about half of those members are from El Salvador.

In some cases, closed shops keep the union intact but pose different problems. "I have nothing against them, but these people are less likely to fight. . . . For a lot of them this money is more than they ever had. . . . But District residents are more apt to complain. They want to fight and change; they're used to higher standards," says Smiley. He says 10 percent to 15 percent of his membership is new immigrants.

But for many other unions, organizing the newcomers is not an easy task. McDonough says local 82 had not tried to organize the employes at Clean Aircraft because of a "communication and language problem." And a Hispanic union organizer hired last September by the Washington Building and Construction Trades Council, who did not want to be identified by name, says his job has been "a very frustrating experience."

Partly, "it's a lack of understanding as to what the union is," says council president Robert Myers.

If the laborers are undocumented, it increases their reluctance to join a union. "They have no benefits, they don't speak English and they get no advice. They're totally job-scared," says Myers.

Myers, for his part, says he has detected little serious resentment toward the immigrants by native-born Americans, who tend to blame the employers rather than the newcomers for loss of job opportunities. "There really isn't that general feeling of animosity to individual Hispanics. They're not blaming the Hispanic people."

Rather, construction laborers are puzzled at how the non-union workers survive on salaries, which Myers says range between $5 and $7 an hour, when the prevailing union wage is $13. " Our members say, 'How can they do this? How do they support a family on this? How can you live in the metropolitan area at $4 to $5 an hour and feed a family, too?' They say, 'That Hispanic guy, he's crazy. He's out of his mind to do this.' But they know there's some reason for them to come and take these jobs."

Squeri, of the Arlington refugee program, says she has not encountered any problems between the refugees she places and Americans already on those jobs. And Le Xuan Khoa, director of the Indochina Refugee Action Center, says his community has not reported any incidents.

Bertha Street, who lost her job along with Lydia Jackson, perhaps sums it up best: "Now I'm going to be like Nixon and make one thing perfectly clear," she says. "I'm not against the employers hiring them. But why do they hire all of them and none of us? We've got to make a living too. I don't mind working with them. I'll work with any color. I just don't want them to put me out in the street."