Thousands of undocumented immigrants who have little hope of ever becoming legal United States residents are forming a perplexing new class of poor in the Washington area.

In the past few months, as the U.S. Immigration and Naturalization Service has begun imposing sanctions against employers for hiring illegal immigrants, social service officials, police and community leaders have been speaking with increasing urgency about the desperate conditions of these newcomers and the future they may face.

They note these immigrants' rising mental-health problems and other medical difficulties. They see increasing homelessness and crime in the Adams-Morgan and Mount Pleasant areas of the District, where the heaviest concentration of illegals lives. And they worry that as the illegals find themselves with more idle time and less income, their problems will worsen.

Most of these newcomers are from rural El Salvador, without families, with little or no education, and already profoundly troubled by the effects of war and dislocation in their homeland.

The prospects for this group stand out bleakly amidst the success stories and high expectations of other recent arrivals here, who were fortunate enough to arrive at a different time, under different circumstances.

The primary disadvantage of the depressed group is that they fit none of the immigration law's criteria for legal status in the United States. Unlike tens of thousands of Indochinese, Nicaraguans, Ethiopians and Eastern Europeans, they do not qualify for refugee status because they fled a noncommunist regime, leaving for "economic" reasons, U.S. officials contend, rather than out of a fear of persecution.

Nor are they eligible for amnesty under the new immigration law. An estimated 90 percent of the Salvadorans arrived here after January 1982, the cutoff date for amnesty eligibility. Many who claim they arrived before then lack the documentation to prove it.

While many still manage to hold on to jobs, many others are finding it increasingly difficult to do so. The INS has already hit two Washington area employers with fines totaling $25,000 and officially warned two dozen others.

Finally, because these residents are in the country illegally, they cannot receive the federal benefits that make it easier for other poor people to survive. Despite some early thought that some of these illegal immigrants would return home, it is widely believed that most will not.

Several recent studies have warned that unless the needs of the illegal immigrants are addressed more adequately, by offering more services or allowing them to work, their poverty will deepen and the eventual financial and social costs to the public at large will increase dramatically. Similar concerns have been raised in other cities with large concentrations of illegal immigrants, including Los Angeles, Houston, New York and San Francisco.

"The long-term effect may be to impoverish a large segment of the Hispanic community and intensify the need for social services," warned a 1987 report by the United Way of the National Capital Area.

Estimates of the number of illegals here range from 70,000 to twice that number. The U.S. Immmigration and Naturalization Service offers the lower figure and the Metropolitan Washington Council of Governments and local social service agencies insist it is far larger.

Already, health and social service providers are seeing mounting evidence of the consequences of the new immigrant underground.Dr. Ricardo Galbis, director of the Hispanic mental health clinic Andromeda, says there is an increasing number of Salvadoran patients with severe mental health problems. The strain of looking over their shoulders, of being powerless to deal with landlords and employers and others, combined with traumas experienced in their homelands, is causing increasing problems of domestic violence, alcoholism and suicide, he said.

In a just-completed survey of 72 Salvadoran adolescents in Adams-Morgan, 81 percent of the youths said they had been exposed to violent deaths, bombings or torture in El Salvador. As a result, most said they had reccurring bad memories, nervousness or illness, according to the survey, sponsored by the D.C. Office of Latino Affairs. About 92 percent of the youths said alcoholism was a problem in their families; 77 percent said domestic violence was a frequent problem; 75 percent said child abuse was a problem. The Rev. Kevin Farrell, director of the District's Spanish Catholic Center, said organizations working with the illegal population are overwhelmed with the increasing demand for food, shelter, legal counsel and medical assistance. Requests for service at his center have multiplied from 7,000 in 1980 to 29,000 last year.

Other social service agencies report increases of 300 to 500 percent in services provided in predominantly Hispanic neighborhoods since 1982. Employment officials say almost all of the undocumented workers are unemployed and underemployed. Those willing to risk penalties now imposed under the law to hire illegal help usually do so because they pay them little money for long hours. Local officials say illegal immigrants who do work often have cleaning, labor, and cooking jobs with no benefits and wages at or below the poverty line. Those who work with the homeless say they are seeing growing numbers of Salvadorans sleeping on the streets and seeking room in shelters. Police estimate that at any given time 1,500 people -- most of whom are Hispanic -- live in the streets, parks or vacant houses around Adams-Morgan and Mount Pleasant.

Even those immigrants who have housing are often living in crowded, unhealthy conditions. From 1985 to 1987, the number of people annually seeking help from Adelante, a bilingual housing counseling agency in Adams-Morgan, doubled to almost 3,000. Judith Arandes, Adelante's director, said the severe shortage of apartments renting for less than $600 a month hurts all poor people, but for illegal immigrants, it is even worse: They are ineligible for federal subsidies and landlords often overcharge them, threatening them with eviction because they often crowd 10 relatives and friends in one- or two-bedroom apartments. The amount of crime in their neighborhoods is believed to be unusually underreported, because illegal immigrants are afraid to call police.

"Once the Poles and the Irish got off at Ellis Island, they were okay. They lived in slums, but they were different from these people {illegal Hispanics} who have no rights," said Farrell, executive director of the Spanish Catholic Center, a major provider of services to Washington's illegal community. " . . . If someone beats them up in the street, they are not going to call the police. It's a terrible situation. We have created a whole new subsociety, a subculture, an underground society that exists outside the laws."

Police Officer Arturo Sylvester, whose glass office looks out onto the Adams-Morgan intersection of 18th Street and Columbia Road NW, pointed to small clusters of young men walking down 18th Street, and said: "That's the undergroud that's harder to see. They don't look like derelicts, you don't see them panhandling. But what are they doing at 11:30 in the morning? They are not at school, they're not working. Some of them walk around all day long.

"Their sisters might do housecleaning and support them. But we don't know how they are surviving," Sylvester said. "If they work, it's under the table. We know very little about them."

What is known is that they are young and not well educated. A report entitled the National Hispanic Agenda '88 says that 45 percent of the Hispanics in this country are under the age of 19 and that about 50 percent of Hispanic youths drop out of school, a rate higher than that of any other major American group.

"They are struggling with English and dropping out of schools," said David Harrington, a consultant for the new District survey of adolescent Salvadorans. Without jobs, a support network and professional help, Harrington said these youths plagued with memories of war and death "run the risk of alcohol abuse, depression and suicide."

This year the federal government will spend $7.5 million -- about $2,000 each -- on the 3,500 official refugees in the District, Maryland and Virginia.

Illegal immigrants are eligible for aid from state and local governments, but not the federal government. Local budget officials say it is impossible to know how much money is spent on services to illegal immigrants, because undocumented persons do not announce their status when seeking help from city clinics, hospitals or drug rehabilitation centers.

However, many illegal immigrants use services at centers in Adams-Morgan, where administrators speak Spanish, and an examination of government funding for clinics and centers in the Adams-Morgan area shows less than $5 million is spent on facilities and services there. The D.C. Office of Latino Affairs spends an additional $1.9 million on services for Hispanics and uses a lot of muscle in getting voluntary help and donations.

Still, compared with the District's current $944 million human services budget and the millions the federal government spends on the relatively small number of refugees, the amount spent on undocumented residents works out, as Harrington put it, "to about a dime."

"It's not only absolutely unfair, but it's going to cost us," said Maria Elena Orrego, director of the nonprofit Family Place in Adams-Morgan, which offers prenatal care to pregnant women. "The money we give to refugees goes a long way. It helps them become productive members of society. But we give undocumented people nothing . . . . We are going to be faced with lifelong problems because we are not caring for the children of parents who are ineligible for services."

Andromeda, the only clinic offering mental health services for illegal Hispanics, last year found its 18th Street offices overrun with 8,400 patient visits. It can afford to employ only one full-time psychiatrist.

The Columbia Road Health Services, a major medical care provider for illegal aliens, had to shut down admissions periodically last year because it could not handle the demand. Its part-time medical staff amounts to two doctors who care for about 300 patients a week.

Ellen Martin, director of Columbia Road Health Services, said there can be two Hispanics sitting in the waiting room with similar medical problems, but if one happens to be a Nicaraguan refugee and the other an undocumented Salvadoran, the Nicaraguan often gets quicker care because federal funds are available.

"If they are illegal and they have to go to the hospital, we have to put a package together for them," Martin said. "We have to find someone to pay for the anesthesiology, the doctors, if there is any kind of special care. Of course if it's an emergency, we can bring them to the hospital, but even then, they {the illegal immigrants} get bare-bones care."

"Let's face it, there are two levels of health care," said Galbis, director of Andromeda. "If you have money and know the ropes you get care. Most illegal immigrants don't even speak English."

The National Institute of Mental Health estimates that 15 percent of the general population has mental health problems and this percentage is thought to be significantly higher for illegal arrivals. Galbis estimated that there are 15,000 to 20,000 immigrants in Washington who don't get the mental health help they need.

Tami Ito, a researcher who compiled the data of the District's new psychological and health survey of Salvadoran youth in Adams-Morgan, said "the reason we looked at this population is that we could find very little objective data. We knew about them anecdotally, but people want numbers before they give money and start programs to help these people."

Recently, Galbis lifted a report on his desk outlining the medical history of a Hispanic mother who had just attempted suicide. Her problems started, Galbis said, when she began taking eight Advil tablets a day for pain, and continued every day for years. "They ate away at her stomach lining. Nobody told her not to take so much of them. Now she can't keep anything down." And that severe disorder, Galbis said, was only one of her problems.

Orrego, from the Family Place, told a recent D.C. health conference about an infant who died because his Spanish-speaking parents did not understand when they were supposed to give the baby medicine prescribed to prevent seizures. Said Orrego, "If there were enough places with translators, this wouldn't have happened."

The Metropolitan Washington Council of Governments, after studying the problem, offered four remedies: have local governments make more resources available to undocumented persons; make the eligibility for local services clearer; increase the bilingual staffs at service centers; and begin aggressive outreach campaigns. A Montgomery County task force is studying the same problem and is expected to issue a report in the coming months.

As the illegal immigrants become more desperate many are worried that they will react more desperately. As the 1987 United Way report warned: "It will be exceedingly difficult, if not impossible, for them to support themselves in a lawful way."

Virginia Maldonado, owner of Los Gemelos gift shop in Adams-Morgan and a legal Salvadoran immigrant, said those who came from her homeland illegally are not going back. They paid small fortunes to cross the Rio Grande and make it to Washington. If they are not given the means or the jobs for food and shelter, she said, "There will be trouble. They will rob the stores. They will get money some way. The government is pushing them to do something bad."

In the District survey of Salvadoran youths, 63 percent of those interviewed said they "have problems" with blacks. Rivalries between blacks and Hispanic, Galbis said, could cause " 'West Side Story' all over again."

"I don't think there will be riots," said Raul Yzaguirre, president of the National Council of La Raza, a Hispanic advocacy group. "But if we drive these people into the choice of doing nothing at home or making it in the underworld, even the most law-abiding person when backed up against the wall, will resort to making a living the best way they can." NEXT: Politics: Blending In