In a ruling that could have major implications for the Washington area's large Salvadoran community, a federal immigration judge has told the Immigration and Naturalization Service it cannot order three persons back to El Salvador as long as it continues to be torn by civil war.

The decision by Immigration Judge Paul A. Nejelski was "a legal as well as moral victory" for Central American refugees, said William Van Wyke, the attorney for the three Salvadorans.

The ruling could reopen debate over whether the United States should continue to deport Salvadorans who are unable to prove that they are specifically targeted for harm in their Central American country, Van Wyke said.

Other immigration law experts, including an INS spokesman, took a more cautious view and noted that Nejelski, one of two immigration judges in the Washington area, has issued a number of controversial rulings regarding Salvadorans. Nejelski's rulings "have been puzzlers in the past," said INS spokesman Duke Austn. "This one is another puzzler."

The INS has appealed most of Nejelski's rulings, but, in what some of the lawyers described as a rebuff to the INS, the Board of Immigration Appeals has refused to consider the appeals on an expedited basis.

Because an estimated 50,000 to 90,000 Salvadorans are believed to have settled here, some refugee experts said Nejelski's decision could have a major impact locally. The Washington area is believed to have the nation's second largest Salvadoran population; Los Angeles has the largest.

If the decision is upheld, it could help the thousands of refugees who have been deported because they could not show the threat of a "well-founded fear of persecution" in El Salvador. Last year, about 14,000 Salvadorans applied for asylum, but the INS granted it to only 337, or 2.4 percent.

Immigration lawyers have noted that a similar number of Nicaraguans sought asylum, but 3,617, or 25.6 percent of them, won it last year because of a directive written by former attorney general Edwin Meese III. Some INS critics have said the Meese action illustrates how the INS has showed favoritism to refugees from a country whose government the Reagan administration opposed.

Arthur C. Helton, director of the refugee project for The Lawyers Committee for Human Rights in New York, predicted the Nejelski ruling would become a factor in congressional hearings this fall because it supports a point that a number of members of Congress have been attempting to make through refugee legislation.

In his 15-page decision, Nejelski rejected asylum requests from three members of a Northern Virginia family who had fled from El Salvador's Usulutan province, a region torn by civil war.

Describing the family's tale as one of "murder, rape and destruction," Nejelski held that "under customary international law they have a right not to be deported to El Salvador as long as the current civil war continues."

Nejelski, who has been sitting as an immigration judge less than a year, said the INS could deport the family -- a 57-year-old grandmother, her 33-year-old daughter and the daughter's 3-year-old son -- to "a third country which is not at war and which will accept them." Immigration lawyers said that means that the government realistically will be unable to deport the family as long as the fighting continues or unless the Board of Immigration Appeals overturns the judge.

The INS has until Sept. 6 to decide whether to appeal the ruling, and Van Wyke said he assumes the INS will appeal because the ruling is contrary to a decade of federal policy, which holds that only refugees who can prove they would be subject to specific threats should be allowed to stay in the United States.

"The importance of the judge's ruling is saying we have a responsibility to people who flee war," Van Wyke said. But getting the judge to accept that view proved to be "the stickler," the lawyer said.

Van Wyke said he had argued the point without success in previous cases and had the testimony of former United Nations refugee experts to support him in the latest case. Nejelski noted that the INS had failed to rebut some of Van Wyke's arguments.

Nejelski also pointed to the current crisis in the Persian Gulf, noting that the United States had "invoked international law against armed aggression, against hostage taking and against violations of diplomatic immunity.

"In the current case involving El Salvador, is it unreasonable to expect this country to follow the clear dictates of international law against the forced return of endangered civilians to a country at civil war? Or, is international law a one-way street in which the United States of America claims only rights but does not assume any responsibilities?"