WACO, TEX., MARCH 22 -- Tibetan chants rose across scrubby central Texas farmland early today as federal officials intensified their psychological assault on an armed religious sect by broadcasting through loudspeakers the meditative prayers of monks who follow the Dalai Lama.

The droning mantra continued until 3 a.m., on a night when FBI negotiators also beamed intense spotlights into the windows of the Branch Davidian compound near here.

The tactics marked the FBI's clearest use yet of psychological warfare against cult leader David Koresh and 95 followers who remain in their well-armed complex 22 days after a gun battle left four Bureau of Alcohol Tobacco and Firearms agents and at least two cult members dead. The shooting started as an estimated 100 armed ATF agents tried to serve a warrant to search for illegal weapons.

The FBI has turned less-intense lights on the compound for many days, but officials said that was purely a defensive measure to prevent those inside from monitoring the movement of federal patrols.

They also have broadcast frequent messages over loudspeakers, but only, they said, to ensure Koresh could not withhold information from his followers about their legal status or opportunity to leave without being harmed. They have cut off the electricity, possibly disabling a pump and depriving the group of any water except rainwater, which officials said they believe is being rationed.

But Sunday night, like an overbearing neighbor, the FBI was simply trying to mess with Koresh's mind.

"This is part of an escalation of the pressure," FBI spokesman Bob Ricks said at a briefing this morning. FBI tacticians had debated serenading Koresh with "Achy Breaky Heart," a popular country line dance song, but decided the Tibetan chants would be more annoying.

One terrorism expert said it seemed the FBI was "trying to psychologically separate Koresh and those who would want to leave" by proving their leader a "mere mortal" who cannot control events, said Robert H. Kupperman, an analyst at the Center for Strategic and International Studies.

Because the group has been isolated and self-sufficient for so long, however, it is uncertain whether such harassing techniques will work.

Koresh could just as easily use the standoff to "reinforce with followers that they are being persecuted by officers of a decadent society," said the Rev. Daniel C. O'Connell, a psychology professor at Georgetown University.

Ricks said the stepped-up tactics were used because officials felt Koresh reneged on a promise to arrange for a "substantial" number of his followers to leave the cult this weekend. FBI negotiators scaled back their activity on Friday night and Saturday out of deference to the Davidians' Sabbath, when Koresh said he was going to gather his flock and prepare them to leave.

Instead, however, only a trickle of mostly elderly men and women left the fortress, nine in all over three days. Though the wife of one of Koresh's chief assistants was in that group -- a positive sign -- Ricks said there is concern the messianic cult leader is mostly letting out people who would be a liability during either another gun fight or a sustained siege. Four of the seven people released Sunday are over 60, and another was immediately hospitalized with a heart condition.

"The ones who are being released are the ones who do not necessarily supply them with any benefit," said Ricks. "The nucleus of control and power within the compound remains."

Koresh eventually started complaining about the noise, but Ricks said the FBI left the tape running, and plans to do more of the same until the talks get back on track.

Though their chants can sound grating and repetitive to listeners, Buddhists consider them sacred sounds "that have a kind of cleansing, or therapeutic, power," said James Breckenridge, a professor of world religions at Baylor University here.

They can be a single sound like "Om," or short phrases like "Namu Amida Butsu," a chant used sometimes in Japan, he said.

In court today, U.S. Magistrate Dennis Green held initial appearances for eight of the nine cult members who exited over the weekend and ordered them held in the McLennan County Jail until a full hearing. The federal agents want them all held as material witnesses to the Feb. 28 gun battle; no criminal charges have been filed yet.

The 23-day-old confrontation involves a who's who of law enforcement agencies with officials investigating a potpourri of possible offenses, ranging from murder to whether U.S. immigration laws have been violated.

For example, the Immigration and Naturalization Service began an investigation prior to the raid after being informed that there were illegal aliens in the compound, said agency spokesman Verne Jervis.

"Based on the information we have, there appears to be 40 or more {illegal aliens}, most of whom had temporary visas expire," Jervis said.

Staff writer Pierre Thomas contributed to this report from Washington.