A racially mixed jury began the final closing out of an era of "dynamite and darkness" here with the murder conviction today of a former Ku Klux Klansman in 1963 bombing of Birmingham's 16th Street Baptist Church.

Robert Edward Chambliss, 73, was convicted of first-degree murder and sentenced to life imprisonment for the death of Carol Denise McNair, one of four black girls killed when a powerful dynamite bomb ripped through the church basement where they were changing into their choir robes.

The jury of nine whites and three blacks handed down its verdict on what would have been McNair's 26th birthday.

Alabama Attorney General William Baxley, who personally prosecuted the case in state circuit court here, said after the trial that the former Birmingham garage mechanic was the ringleader of a group believed responsible for the bombing.

State and local authorities said today that indictments will be sought soon against at least four others whom investigators now believe they can prove were part of the group thought responsible for the bombing.

"Baxley told the jury Thursday he would have sought the death penalty against Chambliss if it was allowed under Alabama law. The church bombing, he said, "was not just heard in Birmingham but was heard around the world, and the people of Alabama have been a long time recovering."

John Jung, a member of Baxley's prosecution team, said after the guilty verdict against Chambliss, "The Ku Klux Klan has been exposed once again as yellow-bellied cowards who operate with dynamite and darkness."

Chambliss, who was free on $20,000 bond, also is charged in the deaths of the other three girls in the Sept. 15, 1963, blast. They are Addie Mae Collins, Carol Robertson and Cynthia Wesley.

The jury deliberated slightly less than seven hours Thursday and today before reaching the guilty verdict. Jurors said after the trial that they voted 11 to 1 for a guilty verdict within two hours after retiring Thursday and that the lone holdout vchanged her vote about 10 a.m. today.

During the jury's reading of its verdict and recommendation for a life sentence, Chambliss showed no emotion. Later the former Klansman stood before Alabama Circuit Court Judge Wallace Gibson and said, "God knows, your honor, I never in my life killed anybody."

Chambliss' attorney, Art Hanes Jr., immediately filed an appeal. Hanes said he would challenge the verdict on several grounds, including the 14-year time lapse between the bombing and Chambliss' arrest and the fact that Alabama law prohibits anyone over 70 from sitting on a jury.

Among the most damaging testimony against Chambliss was that of his niece, the Rev. Elizabeth Cobbs, she told the court during the second day of the four-day trial that Chambliss had confided to her on the day before the bombing "I've got enough stuff to flatten half of Birmingham."

Other witnesses testified seeing Chambliss with what looked like bundles of large firecrackers at his home several weeks before the bombing.

According to Cobbs, on the eve of the bombing Chambliss said, "Just wait until tomorrow morning and they'll beg us to let them segregate."

Cobbs testified that her uncle once said after the blast that the bomb "wasn't meant to hurt anybody. It didn't go off when it was supposed to."

Ironically, the church bombing aroused such horror even among archsegregationists here that it brough an end to a wave of nearly 50 racially oriented bombings that swept this gritty Souther steelmaking capital during the 1950s and early 1960s.

Following the blast, Birmingham became the focal point of desegregation efforts in the South. In addition, the FBI poured nearly 200 agents into the city in an effort to find those responsible for the church blast.

While FBI investigators gathered nearly 200 volumes of material on the bombing, a number of local law enforcement officials criticized the bureau for not sharing its information with state and local police.

A senior FBI official here said recently that bureau officials had presented their findings to the Justice Department but had warned that potential witnesses would probably be too intimidated to talk.

The Justice Department never pressed any charges in the case. But Chambliss was arrested in October, 1963, on a charge of possession of dynamite. He was acquited on an appeal of a conviction in Birmingham city court. Later there was some criticism by federal agents that the arrest had ruined the government's case.

Baxley obtained the FBI's records on the case in 1975 - four years after requesting them from the Justice Department. He claimed the case was broken after reluctant witnesses agreed to talk.

Baxley said Chambliss also told police in 1975 and late last year he had some dynamite before the bombing.