A 22-year-old Reston man, who was convicted last month of raping a woman in Falls Church, pleaded guilty yesterday to a second rape in the Reston area.

Raphael J. Boyd had pleaded innocent but reversed his plea yesterday in Fairfax Circuit Court and admitted that he raped and beat a 52-year-old woman in a more than two-hour-long assault in her Reston townhouse last Dec. 1.

Boyd's court-appointed attorney, Mark Yeager, told Judge F. Bruce Bach yesterday that Boyd switched his plea because of "absolutely overwhelming evidence" against him, including his fingerprint on a wooden art object, shaped like an artichoke, that was used to hit the woman in the head.

Yeager argued that Boyd's previously insistent denial of his involvement in the two rapes, "in the face of . . . an unbelievable amount of circumstantial and physical evidence" indicates Boyd may have been insane at the time of the offenses. Bach ordered Boyd to undergo psychiatric examination before a June 24 sentencing hearing.

The decision to enter the guilty plea came after a marathon seven-hour discussion last Friday with his client, Yeager said in an interview yesterday. Boyd pleaded guilty to six charges in connection with the rape of the woman and burglary of her house, three of which carry possible life sentences.

Before Boyd entered his guilty plea, the rape victim yesterday detailed her more-than-two-hour ordeal in which she said Boyd told her at one point, "I am going to kill you."

The woman, questioned by assistant commonwealth's attorney Chanda Myers, said Boyd apparently gained entry into her townhouse and was waiting, crouched in the dark, when she returned from an aerobics class about 8 p.m. Dec. 1. She said he beat her with his fists and stuck her with a screwdriver for about an hour, then wrapped her head with thick tape, tied her arms and legs to a bench and raped her.

Boyd then ransacked her house and escaped in her 1972 Mercedes-Benz, the woman told the court.

"Is that what happened?" Bach asked Boyd at the conclusion of the hearing.

"Yes, it is," Boyd said in a barely audible voice.

A jury earlier this month found Boyd guilty of raping a 31-year-old Vietnamese woman and recommended a term of life imprisonment for rape and an additional 30 years for kidnaping and robbery in connection with the attack. Sentencing in that case is scheduled for July 1, at which time the judge could reduce, but not increase, the sentence recommended by the jury.

Until last Friday, Boyd accused police of "framing" him for the crimes and denied any role in the incidents. The earlier trial revealed Boyd was one of a number of black men stopped and questioned at random by police during their investigation of the rapes, one of the most intensive investigations conducted by the police department in recent years.

Fairfax County police announced last March that they had ended their investigation into rapes in the Reston area with the indictment of Roland V. Thompson 24, in connection with the rape last January of a Vienna woman. Thompson is scheduled to stand trial on that charge next week.

Separate rape charges against a third man in connection with an assault in Reston were dropped after the victim failed to identify the man as her assailant.