There's nothing unusual about celebrities promoting their faith - think Madonna and kabbalah, Richard Gere and Buddhism, Muhammad Ali and Islam - but the Church of Scientology's Celebrity Centers have been unusually adept at cultivating entertainers such as actor Tom Cruise.

It was no ordinary celebrity feud when Cruise criticized Brooke Shields for taking anti-depression drugs, then berated "Today" host Matt Lauer for suggesting that psychiatric treatment might help some patients.

This was, rather, the latest round in a long-running campaign against psychiatry and the pharmaceutical industry by this expanding, Los Angeles-based religion, which has been immersed in controversies over its 51 years of existence.

Scientology and psychiatry offer directly competing explanations of the source for mental problems and techniques to deal with them.

Scientology was created by science fiction writer L. Ron Hubbard. In "Dianetics" (1950), Hubbard said the "thetan" (soul) suffers from negative "engrams" implanted in this life and innumerable past lives - the church avoids the word "reincarnation."

Scientology "auditors" help clients work through problems using an "e-meter," similar to a lie detector. They seek a state called "Clear" and then advance through various levels of "Operating Thetan."

The church charges that psychiatry "does not meet any known definition of a science, what with its hodgepodge of unproven theories that have never produced any result." It considers reliance on psychotropic drugs as dangerous as past treatments like electric shock or lobotomies.

The American Psychiatric Association's president said last week it was irresponsible for Cruise to "deter people with mental illness from getting the care they need." The association said "rigorous, published, peer-reviewed research clearly demonstrates" that psychiatric treatment works.

Hubbard died in 1986, but his church has continued to find believers and court controversy.

Over the decades, Scientology has been the target of - and initiator of - an unusual number of legal and rhetorical assaults. These have involved not only psychiatrists but disgruntled dropouts and government agencies, first in the United States and then overseas as the church's missions expanded.

In recent years, conflict with Germany's government has been particularly heated, though the church reports recent court victories.

An epic struggle with America's Internal Revenue Service ran 39 years and ended with a 1993 grant of tax exemption. At issue was a basic question: What defines a religion anyway?

David Bromley, a Virginia Commonwealth University sociologist, says Scientology posed a complex problem because it didn't "fit the standard religious model" and "had elements of religion, elements of a business, and started as Dianetics therapy."

To J. Gordon Melton, editor of the "Encyclopedia of American Religions," a religion deals with ultimate life questions "beyond the limits of science that we need answers to" and Scientology qualifies - but not, for example, Freemasonry or Werner Erhard's est training.

Melton categorizes Scientology as a "psychic New Age" faith akin to the Gnostic heresy expelled by early Christianity. He says Gnostics see "the soul trapped in the body and forgetting who it is," and offer tools for escape into "divine status."