ROCHESTER, N.Y. (AP) _ A former Communist Party member who fled his native El Salvador three years ago apparently has slipped out of the United States before a judge could rule on government attempts to deport him, a sanctuary worker says.

Isabel Morrison of the Rochester Sanctuary Committee said Monday that Alejandro Gomez, 44, apparently left the country with his family after writing a letter saying he and his wife had lost faith in legal attempts to remain in the United States.

''They were concerned for their children, that their lives had been in upheaval for the last three years,'' said Ms. Morrison. ''I think they really did lose confidence in our justice system.''

Ms. Morrison said that for the family's safety, she didn't want to speculate on when they left or where they may have gone. But Benedict J. Ferro, district director for the Immigration and Naturalization Service in Buffalo, said he believes the family went to Canada on Saturday.

Gomez had been portrayed by the sanctuary movement as a symbol of unfair treatment by the U.S. Immigration and Naturalization Service. The government, on the other hand, said he should be deported as a national security risk.

Gomez testified in a celebrated sanctuary movement trial in Tuscon, Ariz., in May. Defendants in the case were recently sentenced to probation for illegally transporting aliens.

At a deportation hearing in Buffalo last month, Gomez admitted having been a member of the Communist Party of El Salvador in the 1960s and receiving military training with his wife, Leticia, 41, in Cuba.

But he said he had not been a Communist since 1968 and said his role as a union leader led him into conflict with what he said was the anti-union attitude of the government in El Salvador.

He testified to having been arrested four times, imprisoned without charges, and beaten.

Gomez, his wife and four children fled El Salvador in 1983 and eventually came to Rochester. They had been living in an apartment at the Downtown United Presbyterian Church since June 1984.

Immigration officials arrested him near the church May 23. At the deportation hearing, he was accused of being an illegal alien and a national security threat. Government lawyers said when he applied for asylum in 1985, he denied having been a member of the Communist Party.

Gomez tearfully appealed to Immigration Judge Gordon W. Sacks that he not be returned to El Salvador. ''I could be assassinated - I, my children, my wife,'' he said.

Members of the Rochester Sanctuary Movement rallied around Gomez at the time of his arrest, raising nearly $50,000 for a bond in 24 hours. They also showed up in force at his deportation hearing.

Asked how members of the movement felt now that the Gomez family apparently has fled the country, Ms. Morrison said, ''The biggest feeling is relief that they are safe. Of course, there's also a feeling of loss and grief because we've become so fond of the family and will miss them so much.''