Acting Archbishop Arturo Rivera y Damas, whose predecessor was assassinated a little more than a year ago, today called on Salvadoran authorities to investigate diligently the latest apparent attack on his church -- the disappearance of a U.S. Maryknoll priest.

Rivera y Damas termed the disappearance here a week ago of the Rev. Roy Bourgeois, 38, of Chicago, a "painful case" and urged immediate government action.

"To date there has been no information about him," the Salvadoran prelate said. "He has not been found either alive or dead."

Bourgeois' disappearance has revived bitter memories here of the murder of four U.S. churchwomen in December, two of the Maryknoll nuns. The government has yet to find those responsible, and it is widely believed by observers, including some U.S. diplomats here, that members of El Salvador's armed forces were responsible.

In El Salvador, where the toll of unsolved disappearances and assassinations has been between 100 and 200 a week for 18 months, to be missing for a week is to be presumed dead.

So far six U.S. citizens have been killed in El Salvador. Two U.S. labor union officials advising the land reform program here were gunned down in a hotel restaurant in January. Twelve priests have been killed in the past 18 months.

Before becoming a priest, Bourgeois served in the Navy in Vietnam and had since devoted himself to the nonviolent defense of human rights.From 1972 to 1977 he was a missionary in Bolivia, where he was jailed for a time. Later he worked in Chicago.

He was also jailed in Washington last year after participating in a series of demonstrations to protest militarism, including pouring blood in the Pentagon.

Bourgeois came to El Salvador April 23 as an interpreter for a television team from Chicago's WBBM, a CBS affiliate. On April 26, after attending Rivera y Damas' mass in the cathedral he told colleagues at his hotel that he was going across the street to a pharmacy to buy medicine for an upset stomach. He never returned. s

There has been widespread speculation that he was kidnaped because of his participation in activities opposing military aid to El Salvador.

President Jose Napoleon Duarte, the civilian head of the shaky junta that rules this war-torn land, has cited Bourgeois' background to suggest in an interview with CBS that the priest might have left of his own accord to seek out leftist guerrillas in the hills.

U.S. officials and the missing priest's colleagues say this is unlikely. The Rev. James Noonan, the president of the Maryknoll order who flew here on the case, said, "I have known him 15 years and I can say this would be utterly contrary to his mode of action."