A legal challenge by a Washington-based hotel and restaurant workers' union has set the stage for an unprecedented judicial review of the government's immigration policies for the estimated 500,000 Salvadorans living illegally in the U.S., according to lawyers and officials involved in the case.

The 10,000-member Hotel and Restaurant Employees Union Local 25, which represents about 1,000 Salvadoran waiters, busboys, cooks and kitchen workers, is asking U.S. District Court here to grant "extended voluntary departure" (EVD) status to Salvadorans so that they cannot be deported while violence continues in their homeland.

The lawsuit asserts that many Salvadoran refugees, who fear death or imprisonment if returned to El Salvador, are wrongly denied asylum in the United States because of political considerations arising from the Reagan administration's support for the Salvadoran government.

In an April 28 ruling that surprised both government officials and union lawyers, District Court Judge Charles R. Richey turned down the government's claims that the union lacked legal standing to bring the suit and that such immigration policies are not subject to judicial review because they are political decisions of the executive branch.

The case is currently in pretrial stages and is expected to be heard in late summer.

"State Department officials were astounded that Richey said it was reviewable," said a high-ranking department official who asked not to be named. "It was very, very unusual."

Robert L. Bombaugh, director of the Justice Department's office of immigration litigation, said yesterday the case is believed to be the first challenge to the government's method of deciding whether to grant EVD status.

The government, through the State Department and Justice's Immigration and Naturalization Service (INS), has granted the temporary EVD designation to some 16 nations since 1960.

EVD status essentially means that all potential deportations involving those nations are put on temporary hold.

Currently, Poland, Ethiopia, Afghanistan and Uganda are the only nations for which this blanket protection applies.

One criterion used by State Department officials in considering EVD status is whether the nation is experiencing "widespread fighting, destruction, and breakdown of public services and order," according to the Congressional Record.

In a letter to members of Congress last year, the department said that "while civil strife and violence in El Salvador continue at distressing levels, conditions there do not, at present, warrant the granting of special status to Salvadorans in the United States."

Local 25's executive secretary, Ron Richardson, said in an interview this week that he decided last October to initiate the suit because a growing number of undocumented workers in the union are afraid of deportation.

"Our people say, 'My father, mother and family will be killed if I go back.' But U.S. officials say, 'Tough luck,' " Richardson said.

"Some are afraid of the left wing. Some are afraid of the right wing. We are not taking political sides," Richardson said. "Some of our people are afraid of both sides."

Salvadorans, estimated to number in the tens of thousands in the metropolitan area, are a growing presence in Washington's restaurant and hotel business, holding jobs from dishwasher to chef at some of the city's finest restaurants.

Most are undocumented workers, but neither the union nor management is obligated by law to check credentials. A bill pending in Congress, however, would impose sanctions against employers who hire workers who lack "green cards" permitting them to work.

Richardson said some employers "prey" on Salvadorans because they know they are fearful of deportation. This "docile worker-syndrome," he said, makes the Salvadorans unwilling to complain about working conditions and reluctant to join unions. Local 25 cited these factors in presenting its legal case.

Richard S. Bromberg and Jose Pertierra, who represent the union through an employer-funded free legal plan, said they believe the State Department refuses to consider EVD status for El Salvador because it would be an embarrassing contradiction to acknowledge the danger of death and violence to returning Salvadorans, while also asking Congress to support the Salvadoran government because it is improving its human rights effort.

The EVD designation is especially crucial to Salvadorans, Bromberg said, because it is "virtually impossible" for them to win political asylum here.

Asylum can be granted if an individual demonstrates "a well-founded fear of persecution on account of race, religion, nationality, membership in a particular social group . . . or political opinion," according to the Refugee Act of 1980.

The government in the past has contended that most Salvadorans come here primarily for economic reasons, not to escape persecution. INS, acting on State Department recommendations, therefore denies the overwhelming majority of asylum claims.

"You have to take a hard look at the question of violence versus persecution," said INS spokesman Duke Austin. Federal law, he said, "is not a 'safe haven' act. It says only if you are going to be persecuted you can come here. It does not say you can come to the U.S. if there is any violence at all."

Only 74 Salvadorans were granted asylum in 1982, while applications by 1,067 were denied, according to the most recent INS figures available. A far greater number, estimated at 24,000, are awaiting decisions because of a backlog of about 18 months. In 1982, 14,078 undocumented Salvadorans were arrested, with 5,131 deported or departing voluntarily.

Last year, a report by the office of the United Nations high commissioner for refugees concluded that U.S. refusal to grant asylum to Salvadorans appeared to be a violation of international agreements on treatment of refugees.

Michael Maggio, a leading Washington immigration lawyer who handles many Salvadoran cases, said yesterday the union's challenge is "a fabulous case . . . because it is the first time the State Department is going to be objectively scrutinized" on important immigration decisions.

Asylum requests and EVD are being "denied for political reasons," Maggio said. "The U.S. has never sent people back to a civil war situation. We do not deport people to Poland and we should not. In Poland, they only put people in jail. In El Salvador, they kill them."

Bromberg said he is handling 60 Salvadoran immigration cases for the union, including 20 persons facing deportation.

The government argued in motions to Judge Richey that the United States would lose credibility internationally if one branch of government overrules another on foreign policy matters.

W. Scott Burke, the deputy assistant secretary of state for asylum and humanitarian affairs, said yesterday that EVD decisions are based on "foreign policy interests, immigration interests and humanitarian interests" as assessed by the secretary of state, who requests EVD status from the attorney general.

Bombaugh of the Justice Department said that the attorney general makes the final decision, but that "no formal procedures or mechanisms" govern the decisions, which are made on a case-by-case basis. "It is a matter of discretion," he said.

"We continue to hold the position that EVD decisions are not subject to judicial review," said Bombaugh, one of three trial lawyers assigned to the case. "This is a case that has a lot of policy implications," said Bombaugh, who added that the government would be claiming executive privilege on some key points during the case.

El Salvador has been considered several times for EVD status since 1981, he said. He declined to discuss the reasoning behind the decisions because of the pending case.