The confession of a Ku Klux Klan member and alleged FBI informer who helped the Klan kill a black man 36 years ago has prompted an internal FBI inquiry into whether the man was an informer at the time of the killing and whether the bureau tried to protect him from prosecution 17 years ago.

The inquiry was prompted by the chain of events set in motion when the Klansman, Henry Alexander of Montgomery, Ala., confessed his role in the killing to his wife just weeks before dying of lung cancer last December. Last month, Diane Alexander got up the courage to write to Sarah Edwards Salter, the widow of the slain black man, to tell her how her husband met his end.

Now Salter, who was 23 years old, a mother of two and expecting a third child when her husband died in 1957, wants to know what, if anything, the government knew about Willie Edwards's death. And the Southern Poverty Law Center, which is representing the Edwards family, also wants to determine whether the FBI can be held financially liable for employing or having a confidential relationship with the self-described killer.

"We were hoping that they would release the records," said Salter, now 59, of Buffalo. "We just want to find out what went down."

In ordering the internal inquiry into the case, FBI Director Louis J. Freeh also said Wednesday that the bureau "will respond as promptly as possible to a request from Willie Edwards's family for information on the case."

According to Alexander's widow and a statement given to authorities 17 years ago by another Klansman, the Klan group led by Alexander abducted Edwards, a 23-year-old Winn-Dixie grocery truck driver, while searching for a black man who they believed had been too friendly with a white woman.

They hit Edwards, threatened to castrate him, then took him to a bridge and forced him at gunpoint to jump. Screaming on the way down, he fell 50 feet into the Alabama River, where his decomposed body was found three months later.

Alexander targeted Edwards and participated in the slaying because "he wanted to be big and important" among his Klan peers, according to a copy of the letter Diane Alexander wrote to Salter.

"I know that your husband died for no reason," she wrote. ". . . Henry played a big part in the Klan. I don't know why God did not let him serve any time in jail for his part, but I do know that Henry was sorry for what he done."

Alabama authorities had no idea that Edwards was murdered until then-Attorney General William Baxley stumbled onto the Edwards case in 1976.

Baxley's investigators were tracking Klan leads in the 1963 bombing of the 16th Street Baptist Church in Birmingham when one of their Klan suspects declared, " 'I got out of the Klan after they killed that Winn-Dixie driver,' " Baxley said yesterday.

Alexander, who had been charged but never tried in several church bombings, was indicted twice in 1976 in the Edwards killing, Baxley said. But both times the case was thrown out because the cause of death could not be proven.

State officials were not allowed to appeal such dismissals, said Baxley. He said he and his staff were "trying to decide what our options were and had about concluded we simply didn't have any."

About that time, Baxley was approached by FBI officials who "told me that Henry Alexander had been their best informant they'd ever had in the Klan and that they would appreciate any consideration" Baxley could give him.

Baxley said the FBI left him with the impression that Alexander had been an informer at the time of Edwards's death, but he did not know for sure.

Knowing the case against Alexander was stalled anyway, and knowing he would need the FBI's help in solving the Birmingham bombing in which four black girls had died, Baxley told the FBI he would drop the Alexander case if the bureau agreed to put its request in writing.

Baxley said the FBI letter is stored in a warehouse with his papers from his days as Alabama's lieutenant governor and attorney general.