Police are investigating an Alexandria physician who allegedly prescribed "a massive quantity of drugs" to Nancy Moffitt, a Falls Church woman who died of a heroin overdose last August, according to an affidavit filed in the Alexandria Circuit Court.

Dr. Joel L. Koslow, an internal medicine specialist practicing at 4921 Seminary Rd., is under investigation, according to an affidavit filed by Alexandria police, for allegedly "prescribing and distributing controlled drugs" to Moffitt "not on the basis of medical need, but upon Moffitt's request."

An Arlington man has been charged with involuntary manslaughter for allegedly giving Moffitt a fatal heroin injection last Aug. 9.

Koslow, 46, a member of Alexandria Hospital's medical staff since 1971, according to a hospital spokesman, could not be reached yesterday for comment on the police affidavit.

For three years prior to her death at 33, Moffitt secured more than 2,750 doses of controlled drugs, including Biphetamine, Quaalude and Percodan, with prescriptions that were written under Koslow's name, the affidavit asserts, quoting William A. Hurst, the investigating officer from the Virginia Department of Health Regulatory Boards.

Assistant Commonwealth's Attorney Randolph Sengel, who has been assigned the case, said he will discuss it next week with police and health officials. Under Virginia law, illegal distribution of controlled drugs is punishable by up to 40 years in prison and a fine up to $25,000.

The State Board of Medicine will also receive a complete report on all drugs Koslow prescribed to Moffitt next week, Hurst said. Eugene Dorson, the State Board of Medicine Executive Secretary, said the board will then decide whether to revoke Koslow's medical license.

The health department investigation began, the affidavit says, after James and William Moffitt, the dead woman's father and brother, found drugs, pharmacy receipts, letters and documents in Nancy Moffitt's home at 2224 Pimmit Run Lane, Falls Church, after she died..

The affidavit also says checks written to Moffitt on Koslow's professional account also were found and one of the letters, written on Koslow's professional stationery, said, "I want you to know how special you are, how much I miss and care for you and love you."

Donald J. Munley, 33, of 860 S. Greenbriar St., Arlington, was charged with involuntary manslaughter Aug. 16 in Moffitt's death. He is free on $5,000 bond.

The affidavit, filed last week by police Officer David B. Goldberger after an Alexandria Circuit Court magistrate granted a search warrant for Koslow's medical office, states that the physician was Moffitt's doctor when she was admitted to Fairfax Hospital in 1982 suffering from a drug overdose.

Hurst said in the affidavit that hospital records show Koslow "continued to prescribe large amounts of . . . schedule II [highy addictive] drugs" after Moffitt was released.