The FBI was aware of a "carefully planned" criminal conspiracy to beat up Freedom Riders in Alabama 22 years ago and was derelict in its duty to prevent the violence, a federal judge ruled here today.

The sternly worded decision, issued in the case of a crippled Michigan man and his late wife, said the FBI even became involved in the conspiracy through the actions of its informers, especially a Ku Klux Klansman named Gary Thomas Rowe who took part in the mayhem at the Birmingham, Ala., Trailways bus terminal on May 14, 1961.

U.S. District Court Judge Richard A. Enslen held the government liable for the FBI's "misfeasance" and said he would proceed to determine damages. The claims total $2 million.

The surviving plaintiff, Walter Bergman, 83, a retired Michigan educator who was battered and stomped at a rest stop in Anniston and pushed around again on arrival in Birmingham, expressed his delight at the ruling. "Without a question of a doubt," he said in a frail but loud voice from his wheelchair, "we have a better America in 1983 than we had in 1961 . . . . Not as good an America as we should have . . . , but we are making progress."

Enslen announced his findings in an 83-page opinion, supplemented by a separate ruling in which he denounced the Justice Department for "flagrant disobedience" in refusing to comply with court orders to submit documents.

"The plot to injure and perhaps kill the Freedom Riders was one which involved all Klansmen in . . . Alabama" as well as police officials in Birmingham and elsewhere in the state, Enslen said.

In fact, he said, Rowe testified of an April 17, 1961, meeting with a Birmingham police sergeant named Thomas Cook about the "reception" that was in store for the black and white civil rights workers bent on integrating bus service in the South.

" 'We're going to allow you 15 minutes,' " Cook was quoted as telling the FBI's top Klan informer. " 'You can beat 'em, bomb 'em, maim 'em, kill 'em--I don't give a damn . . . . There will be absolutely no arrests. You can assure every Klansman in the country that no one will be arrested in Alabama for that 15 minutes.' "

In short, the judge held, reciting this and other incidents, "through its agents, the government not only had knowledge of the far-ranging conspiracy, but knew of the acts taken in furtherance of the plot."

However, the ruling continued, "The FBI did absolutely nothing to prevent or minimize the effects of the conspiracy. In fact, the course of action which the FBI followed served to increase the risk of harm . . . and to assist the conspirators . . . . "

This was so, Enslen said, because the FBI "authorized and approved the actions" of Rowe and "provided critical information" to Cook "despite the bureau's knowledge that Cook was intimately involved in the conspiracy and would use this information to aid that conspiracy."

The opinion contrasts sharply to another federal judge's ruling last week in Ann Arbor that the FBI was not responsible for the 1965 murder of civil rights worker Viola Liuzzo despite Rowe's presence among the Klansmen who killed her. But Judge Charles Joiner said he would have come to "a different result" if he thought that Rowe had shot Liuzzo or had caused the others to do so.

"The facts were very different, the issues were different, and most importantly, the judges were different," said William Goodman, chief counsel in the Bergman case, which was undertaken by the American Civil Liberties Union.

"We were not saying Rowe was a killer or an evil person. We did say Rowe was a violent person and he told the FBI a lot well in advance. They allowed him to participate in the violence. They allowed the conspiracy to go forward. The fault lay not with Gary Thomas Rowe; the fault lay with his masters."

On that score, Enslen stressed Rowe's testimony that he "had been assured by bureau contacts that the FBI would never allow the violence to occur." The government argued that the FBI had told Birmingham police, in general terms, that violence was possible, but the judge held that that warning was inadequate, especially in light of testimony by C.L. McGowan, then the FBI's civil rights section chief.

McGowan testified that he called the FBI field office in Birmingham and told them 'Don't sit on it. You've got to disseminate it even if it blows your informer . . . . ' Protection of the individuals riding that bus was more important than saving one informer."

The court also faulted the FBI for keeping Justice and the White House in the dark about the likelihood of violence. The judge noted testimony by Supreme Court Justice Byron R. White, then deputy attorney general, and by Burke Marshall, then assistant attorney general for civil rights, who said that action would have been taken.

Enslen said possible actions included sending FBI agents to the scene with cameras, making their presence known to the conspirators; informing state and local authorities that Justice knew what was going on, and even calling on federal forces to prevent the violence. The judge noted that the government cracked down effectively in Alabama after the assaults in Birmingham and Anniston and sent U.S. marshals into the South to protect the Freedom Riders.

Enslen also rejected the FBI's claims that it is merely an investigative agency and had no duty to do more. He said what happened in Alabama was clearly a violation of federal law, a conspiracy to deprive people of their rights on account of race.

"As the facts of the case disclose," Enslen said, "the FBI not only received a continual stream of information concerning the plan to interfere with . . . and to injure the Freedom Riders, but had advance knowledge about definite steps taken to put that plan into action . . . .

"If the FBI had transmitted all of its information to the Civil Rights Division of the Department of Justice, that agency could have authorized the prosecution of the suspected perpetrators. However, the FBI did not pass its information to Justice until four days after the assaults . . . . "

Enslen began his opinion with quotations from a speech by Robert F. Kennedy, who was then attorney general, at the University of Georgia law school on May 6, 1961, eight days before the violence in Alabama.

"We will prosecute," Kennedy said of the nation's civil rights statutes. "We will enforce them vigorously."

Enslen observed: "The 'we' presumably refers to the United States, which he represented . . . . "