An Alexandria police officer whose cruiser collided with an auto in Jaunary, killing a 75-year-old woman, was convicted yesterday of speeding and fined $50.

Alexandria General District Court Judge Daniel Fairfax O'Flaherty followed a prosecutor's recommendation that Officer Charles Daniel Keyes be fined $50 instead of the maximum $100 because of a previously unblemished driving record.

According to testimony yesterday, Keys was responding to a purse snatching call Jan. 12 when his police car hit a car driven by Everette Brewer and his wife, Mary Bibb Brewer, at Rte. 1 and Swann Avenue. Mrs. Brewer was fatally injured.

Keyes, whom the judge convicted of driving 60 miles an hour in a 35-mile-an-hour zone, was not using his car's siren and flashing red lights at the time, according to prosecution testimony.

Police regulations require officers to use their sirens and flashing lights when driving above speed limits, and Keyes could be subject to future disciplinary action.

Commonwealth's Attorney John E. Kloch, whose office investigated the accident, said recently that speeding was the only charge that could be brought because there was not enough evidence to warrant others, such as reckless driving or manslaughter. There was no indication, the prosecutor said, that Keyes was weaving in and out of traffic or violating any other traffic ordinances.

Mary Brewer's estate has filed a $500,000 civil damage suit against Keyes and the city. It has not yet been resolved.

Defense attorney George Towner said before yesterday's trial that Keyes "feels terrible about this. It has hurt him very much. It is something he will have to live with for a long, long time." Following the verdict, Towner said he did not know whether his client will appeal.

"This is one of those unfortunate things that can happen when a police officer is performing his duty," Towner said before the trial. "But if he had gone to the accident more slowly, he might have been criticized for that. There were two cars involved here. It is truly, truly unfortunate that someone died," the lawyer said.

Keyes, who pleaded not guilty to the charge, declined to comment yesterday. He had been on the Alexandria force two years at the time of the accident.

The lawyer who filed the suit against the officer said yesterday his client views the accident differently from Towner. "It doesn't make any sense to endanger the lives of innocent people for something like a purse-snatching," said attorney Michael Jamgochian.