A Woodbridge doctor was charged yesterday with dispensing much-needed pain medication to a female patient only after she performed sex acts with him, federal authorities said.

Abhay Vivek Aggroia "sexually exploited" the patient, who had chronic back and neck pain from an automobile accident, according to a criminal complaint and affidavit filed in U.S. District Court in Alexandria. The court documents say Aggroia, who specializes in internal medicine, fondled the woman and then prescribed Percocet pills for her during a series of office visits starting last year. The behavior is alleged to have continued until January.

At one point, Aggroia told the woman that if she wanted more Percocet, she would have to provide "more" for him, the court papers say. When the woman asked what that meant, Aggroia told her in "blunt and graphic terms'' that he wanted oral sex, the papers say. The woman complied during weekly and biweekly visits because she had become addicted to the medication, the court papers say.

Federal officials said they expect Aggroia, 51, to turn himself in to authorities today and to appear in court on a charge of unlawful distribution of a controlled substance. Reached at his office yesterday, Aggroia referred calls to his attorney, who declined to comment.

The court papers say Aggroia had signed a statement admitting to "inappropriate physical contact" with the patient and had acknowledged to authorities that he received oral sex from her.

Aggroia is the second doctor charged in a broad federal investigation into physicians, pharmacists and patients suspected of distributing Oxycontin and other potent narcotics. The other doctor, pain management specialist William E. Hurwitz, was convicted in December of running a drug conspiracy out of his McLean office. He was sentenced to 25 years in prison.

More than 50 people have been convicted in the investigation, which is known as "Operation Cotton Candy.''

U.S. Attorney Paul J. McNulty accused Aggroia of "violating his oath as a physician by demanding sex for highly addictive prescription drugs. He fed his own appetite at the expense of his patient's well-being.''

A copy of the charges against Aggroia will be sent to the Virginia Board of Medicine, which regulates the conduct of the state's doctors, law enforcement officials said yesterday. William L. Harp, the board's executive director, said that he could not comment on any specific case but that doctors who are investigated could face sanctions ranging from a reprimand to revocation of their license.

The complaint and affidavit, filed in court by Assistant U.S. Attorney Gene Rossi, says the patient was referred to Aggroia by Virginia's Medicaid program.

During her first visit, in June 2004, Aggroia rubbed his arm on the woman's breasts as he checked her heartbeat, according to the affidavit written by Dana Crane, a Virginia State Police special agent. He then allegedly had her roll down her pants and asked her to bend over, the affidavit says.

The fondling grew progressively worse, and the woman began performing oral sex about a month later, the affidavit says.