A 23-year-old Providence, R.I., woman, found dead in a Rockville motel the day after she had testified for the prosecution in a trial stemming from her sister's murder, apparently committed suicide, the Maryland medical examiner's office ruled yesterday.

The Associated Press quoted Dr. Virginia Dolen as saying that the woman, Vivian Levy, died of a drug overdose taken several hours after she testified in the prejury trial of Stephanie Walker.

Claire Levy, 24, Vivian's older sister, was found strangled last January in an apartment at 8039 Eastern Ave. in Silver Spring.

Shortly after Claire Levy's body was discovered, Vivian Levy's boyfriend, David Leander Stratmon Jr., 23, of Northwest Washington, was charged with murder.

The charges against Stratmon were dropped after Walker, a key witness, changed her story four times about the events of Jan. 28, 1979. Police then charged Walker with perjury.

A Montgomery County jury convicted Walker of four counts of obstruction of justice in November. Sentencing is scheduled for Jan. 3.

The afternoon after she testified in Walker's trial, Vivian Levy's body was discovered in the motel room by hotel employes and police, who had been notified by her family after she did not return to Providence as scheduled.