The American Civil Liberties Union sued the FBI for $2 million yesterday on charges that the bureau was responsible for the 1965 Ku Klux Klan murder of civil rights worker Viola Gregg Liuzzo.

The suit was filed in U.S. District Court in Detroit on behalf of Liuzzo's five children, whose ages range from 20 to 33 years.

Specifically, the suit asserts that the FBI was responsible for Liuzzo's death through the action - or inaction - of its onetime paid informer, Gary Thomas Rowe Jr.

The suit also accuses "the FBI and the United States of . . . fraudulently concealing the nature of Rowe's involvement in Viola Liuzzo's murder, as well as his relationship with the FBI." The alleged cover-up lasted until Rowe revealed his role before a U.S. Senate panel in December 1975, the suit says.

"We just cannot comment on it," said Robert Hamilton, a spokesman for the Department of Justice, which has jurisdiction over the FBI. "The proper place to respond to this is in the court."

Liuzzo was shot to death March 25, 1965, at the end of a high-speed, 20-mile, nighttime car chase through Lowndes County, Ala. She had gone to Alabama from her home in Detroit to participate in the Selma-to-Montgomery voting rights march. She was 39.

The car from which the fatal shot was fired was occupied by four members of the Alabama Knights, Knights of the Ku Klux Klan, Inc. One of them was Rowe, who had worked as an FBI informer since 1960.

Rowe could have and should have stopped the shooting, the suit, maintains. Instead, he may have actually shot Liuzzo, the suit says.

Rowe has steadfastly maintained his innocence in the Liuzzo killing. However, last year he was indicted for the murder by a Lowndes County grand jury. His trial is expected to take place in the fall.

The outcome of the criminal case, however, will have no direct effect on the suit filed yesterday.

"The suit we filed isn't against Rowe," said Penny Liuzzo, 33, the oldest of Liuzzo's five children.

"Whether or not he pulled the trigger is not the big question. He was working for the FBI when my mother was killed. He was in the car with the others during that terrible chase. . . . He could've stopped it. That's what this suit is about," she said yesterday in a telephone interview.

Penny Liuzzo - who is married, but who insists on using her maiden name "to protect my husband and children" - said her family would not have taken action against the government had it not been for Rowe's 1975 Senate appearance.

"Up to then, based on what we were told, we thought Rowe was the hero. We know different, now," she said.

Three of the dead woman's children, including Penny, live in the Detroit area. One lives in California. The fifth, Thomas, 28, lives in Lowndes County, Ala., "where he can keep an eye on the Rowe case," Penny Liuzzo said.

"Tom just felt that being down there was something he had to do. He's just like his mother in a lot of ways," she said.

Liuzzo's husband, Anthony Sr., died Dec. 10. There are four grandchildren, ranging in age from 4 to 12 years.

Rowe, who now lives in Savannah, Ga., could not be reached for comment yesterday.