In the hush before services begin at a church in Berkeley, Calif., parishioners are hearing a new question: "Is anybody here a government agent? If so, you are advised to leave at this time."

At a recent closed-door meeting in Tucson, a dozen leaders of the American sanctuary movement discussed ways to improve security in churches.

"We're not going to be clandestine or anything like that," one participant said. "This just means we have to ride herd on security. We have to."

What prompted such concerns was last month's indictment of 16 leaders of the American sanctuary movement for conspiracy to transport Salvadoran aliens and the simultaneous roundup of 60 Salvadorans for deportation.

Movement activists said they had long expected a crackdown by the government but nonetheless were surprised by the scope of the indictments and by the extent of government intrusion into houses of worship, which they see as a threat to their constitutional right to freedom of religion.

The indictments capped a 10-month investigation by two federal agents and two Hispanic informers who infiltrated the movement by offering blankets and fruit to members of its "underground railroad" in northern Mexico last spring.

The infiltrators collected 40,000 pages of evidence and taped 100 hours of movement planning sessions, many in Tucson's Southside United Presbyterian Church, which in 1982 became one of the first in the nation to declare itself a public sanctuary for Salvadoran refugees.

Movement leaders say the charges show that the government is entering a new phase in its dealings with those who aid and house Salvadoran and Guatemalan refugees.

"There are a lot of people out there thinking, 'Maybe my turn will come next,' " said Jack Elder, the Roman Catholic director of a Texas halfway house for refugees, who recently was acquitted on charges of aiding Salvadoran aliens and is on trial again on similar charges.

Since Southside and a handful of other churches declared themselves public sanctuaries on March 24, 1982 -- the second anniversary of the assassination of Archbishop Oscar Romero in San Salvador -- the movement has attracted more than 100,000 participants in more than 180 churches nationwide who offer aid and protection to Central American refugees at the risk of violating U.S. immigration laws on transporting aliens.

Activists justify their actions by pointing to the death of more than 50,000 Salvadoran civilians since 1980 and the unwillingness of U.S. immigration judges to grant political asylum. Roughly 3 percent of Salvadoran applicants received asylum last year, compared with 33 percent of Polish and 12 percent of Nicaraguan applicants, according to the Immigration and Naturalization Service.

Administration officials respond that Salvadoran applicants for asylum are fleeing poverty, not persecution, and that violence in El Salvador has decreased in the past few years.

The movement has pushed for the State Department to grant "extended voluntary departure" status to Salvadoran refugees, allowing them to stay in this country until violence in their homeland subsides. The department has granted that status to Poles, Afghans and Lebanese.

That would open the borders to mayhem, said Elliott Abrams, assistant secretary for human rights. "Congress does not want us to suspend our immigration laws for every country in the world that has a lot of violence," he said.

Before the indictments last month, there had been only one other case involving a sanctuary worker, Philip Willis-Conger of Tucson, and a federal judge had thrown it out before trial.

The 16 sanctuary activists indicted in January included some of its most prominent leaders, including Southside's pastor, the Rev. John Fife; James Corbett, a retired Arizona rancher and founder of the "underground railroad;" two Roman Catholic priests; three nuns; Willis-Conger, and Katherine Flaherty, a former Peace Corps volunteer in El Salvador.

"The first column might have fallen," Flaherty said. "But there are columns behind us ready to follow."

Fife said, "It's clear that they didn't have to put infiltrators into our church and Bible study groups. The only basis for that continuing investigation seems to have been an attempt to discredit the movement. Was I sleeping with my neighbor's wife? Were we running some drugs across the border to pay for the sanctuary operation?"

Don Reno, a special U.S. attorney in Phoenix, said the government informer attended sanctuary meetings at Fife's church to gather evidence admissible in court. Particular activists were not targeted, he said.

"We didn't try to make distinctions as to who we arrested. It so happened that the people we indicted were spokesmen and at the heart of the movement."

An INS spokesman said the investigation was "nothing unusual. We have thousands of investigations of smuggling operations under way at any one time."

Yet the INS previously had made a point of distinguishing its position on the sanctuary movement, as opposed to other smuggling operations. Last June, INS Commissioner Alan Nelson said in a five-page memo distributed to U.S. attorneys around the country that the INS had not conducted and would not conduct "special targeting" of sanctuary participants.

"Consistent with past and existing policy, we do not enter into churches," he said in the memo.

Federal agents have yet to arrest a refugee inside a church, and INS spokesman Vern Jervis said that the investigation, which Nelson approved, did not stray from the guidelines set in Nelson's memo.

Sanctuary leaders expressed alarm, however, at a federal roundup of more than 60 Salvadorans in connection with the indictment. Among those detained for deportation hearings was a Salvadoran family that had received a ride from one of the informers to a Phoenix Christmas celebration just days before, according to Flaherty.

That informer, who identified himself as Jesus Cruz, joined the movement in late April, Willis-Conger said, by offering blankets, bananas and oranges to some movement suporters visiting Salvadoran refugees in a Mexican prison across the border from Arizona. Cruz also attended Willis-Conger's October wedding without an invitation, Willis-Conger said.

"It really saddens and amazes me that someone can work with us for 10 months and not understand what we're about to the point where they can turn around and play Judas," he said.