A mistrial was declared yesterday in the case of a former Lorton prison guard and police officer who was charged with rape after a Fairfax County Circuit Court jury failed to reach a unanimous verdict.

It was unclear whether the defendant, Federico Headley, 41, will be retried, although a new trial was scheduled for Dec. 4. A county prosecutor said she hopes to develop new evidence in the case by that time.

The jury's final vote was 9 to 3 in favor of acquitting Headley of one count of rape and one count of breaking and entering with intent to rape in a May 20 assault on a woman in her Alexandria-area hotel room.

Headley, called the "Route 1 rapist" in court by assistant prosecutor Corinne J. Magee, was convicted in two Fairfax trials earlier this fall of attempted rape, two counts of sodomy, breaking and entering with intent to rape, abduction, and two counts of burglary.

The juries in those trials recommended Headley be sentenced to a total of life plus 62 years in prison, and Headley is jailed pending a sentencing hearing Dec. 7.

The jury in yesterday's trial did not know of Headley's convictions.

Headley was arrested after a series of six rapes and assaults in motels in the Richmond Highway (Rte. 1) corridor of Fairfax this summer. Headley, who at one time was a guard at Lorton Reformatory, a police officer in Glen Arden and most recently a guard at a federal prison outside of Atlanta, is charged in two of those incidents.

Circuit Judge Richard J. Jamborsky declared a mistrial and dismissed the jurors at noon yesterday when they reported being irreconcilably deadlocked after eight hours of deliberations over two days.

Magee said after the trial that "at this point, I'm inclined to retry" Headley but said that "if I can't make the case any stronger than it is now, I won't retry it."

She said she hopes police can develop additional physical evidence and witnesses before the trial date.

The victim in the May 20 incident was unable to positively identify Headley by sight, but picked his distinctively accented voice out of a voice line-up, Magee said.

"I think that even though the victim testified she was 100 percent certain about the voice identification, jurors tend to want more than that," Magee said. "They want a visual identification in order to convict somebody on such a serious offense."

In addition to the voice identification, hair and semen samples found in the victim's hotel room were consistent with samples taken from Headley, according to testimony.

Alan B. Soschin, Headley's attorney, called the mistrial "a little frustrating . . . . I can't be ecstatic over a hung jury."

He said the prosecution "didn't have a terribly strong case. And if they try to try it again on the same evidence, I will be a little disappointed."