Scientology officials said that the investigators operated within the law and that the tactics were necessary to counter attacks made over the years by Internal Revenue Service agents and the press.
"When people stop spreading lies about them and stop printing false allegations about them in newspapers, the church will stop using private investigators," said Monique E. Yingling, a church lawyer.
In 1986 the Federal Court of Appeals in Boston said evidence in an extortion case indicated that Scientology investigators had induced witnesses to lie. It identified one investigator as Eugene M. Ingram.
Eight years later, Mr. Ingram was charged with impersonating a police officer in seeking information about a sheriff in Tampa, Fla., while working as a church investigator. He and a Scientology employee flashed badges and told a woman that they were police detectives before questioning her about possible links between a county sheriff and what was said to be a prostitution ring, police records say.
Court officials said a warrant for Mr. Ingram's arrest was still outstanding.
Mr. Ingram had been dismissed from the Los Angeles Police Department in 1981 after accusations that he was involved in running a prostitution ring and had provided information to a drug dealer. He was acquitted of criminal charges in that case.
Elliot J. Abelson, the church's general counsel, said he had used Mr. Ingram often as an investigator and had the highest regard for him. He said the Tampa case was phony.
Richard Behar, an investigative reporter, incurred Scientology's wrath when he wrote a cover article about the church in Time magazine in 1991. The article called the church "a hugely profitable global racket that survives by intimidating members and critics in a Mafia-like manner."
The church and a member sued Time and Mr. Behar for libel, and the company spent more than $7 million defending the cases. The church's suit was dismissed last year by a Federal District Court judge, an action being appealed by Scientology. The individual's suit was settled with a statement but no money.
Mr. Behar contends in a countersuit that even before the article ran, church investigators questioned his acquaintances about his health and whether he had had tax or drug problems. Mr. Behar said that after the article ran, he had been followed by Scientology agents and had been so concerned he had hired bodyguards.
In 1992, Judge Ronald Swearinger of Los Angeles County Superior Court told The American Lawyer magazine that he believed Scientologists had slashed his car tires and drowned his collie while he was presiding over a suit against the church. The church denied the accusations.
In 1993, Judge James M. Ideman was presiding over a suit involving Scientology in Federal District Court in Los Angeles when he took the unusual step of withdrawing from the case. In a court statement, he said he could no longer preside fairly because the church "has recently begun to harass my former law clerk who assisted me on this case."
Kendrick L. Moxon, the church's lawyer in the case, said he had tried to question the former clerk about accusations that there was a framed Time magazine cover about Scientology in the judge's chambers. He said that the former clerk had refused to talk to him and that his subpoena for her testimony had been quashed.
Scientology's tactics in court have also drawn judicial rebukes. Last year, the California Court of Appeal accused Scientology of using "the litigation process to bludgeon the opponent into submission." The Federal Court of Appeals in San Francisco said last year that Scientology had played "fast and loose with the judicial system" and levied $2.9 million in sanctions against the church.
By aggressively pursuing its opponents in court, the church seems to heed the preaching of L. Ron Hubbard, its founder, who once wrote: "The purpose of the suit is to harass and discourage rather than win. The law can be used very easily to harass, and enough harassment on somebody who is simply on the thin edge anyway . . . will generally be sufficient to cause his professional decrease. If possible, of course, ruin him utterly."
One focus of suits by Scientologists was the Cult Awareness Network, a nonprofit organization dedicated to countering religious groups it perceived as dangerous.
Scientology has long regarded the network, known as CAN, as an opponent of religious freedom and a hate group. Church officials said the network used "deprogrammers" to kidnap people in an effort to persuade them to leave small religious groups. Deprogrammers affiliated with the network have been convicted of crimes in connection with efforts to force people to leave religious organizations.
Beginning in 1992, Scientologists filed 40 to 50 suits against the network and its officers, contending that they discriminated by refusing to allow Scientologists to attend conventions or join chapters. Some Scientologists prevailed in court.
Mr. Moxon, who represented many Scientologists, said the suits had been intended to address network discrimination against people who wanted to reform it.
But Daniel A. Leipold, who represented the network, said during depositions in some of the suits that the actions had been part of a campaign by Scientology to destroy the network.
Last year, the network declared bankruptcy after a $1.8 million judgment against it in a suit brought by a young man who had been a member of a Pentecostal group. The jury found that the man had been forcibly detained by a deprogrammer. Mr. Moxon, who represented the man, said that he had taken the case as a religious freedom matter and that his expenses had been paid by the Pentecostal group.
After the network filed for bankruptcy, its name, logo and telephone were bought by a group represented by a lawyer who is a Scientologist. While the church said it had no connection with the purchasers, a brochure mailed by the new Cult Awareness Network in January was a glowing description of Scientology as a means to "increase happiness and improve conditions for oneself and for others."