An internal Alexandria police investigation into the force's handling of a 1975 complaint against former prosecutor William L. Cowhig has been reopened, city officials said yesterday.

The decision to reopen the investigation came after a city councilman noted that news accounts mentioned that more than one police officer may have participated in the Cowhigh investigation.

"We are looking into the allegations," Police Chief Charles T. Strobel said yesterday, confirming that he ordered the internal investigation reopened. "I'm not closing anything that needs to be tied down."

City Manager Douglas Harman said last week that the internal probe into policy handling of sexual bribery charges against Cowhig had been concluded. Harman's statement coincided with the resignation of Capt. Norman E. Grimm, a 26-year police veteran who admitted suppressing a damaging police report on Cowhig.

Cowhig, who resigned last month as Alexandria's commonwealth's attorney, has repeatedly denied the allegations that prompted the investigation that he solicited a sexual favor from the wife of a defendant he was prosecuting. But he reportedly admitted to a police officer that he engaged in some sexual activity with the woman in the suppressed police report.

City Manager Harman said yesterday he was asked to reopen the police internal investigation by City Councilman Donald C. Casey, on the basis of a Washington Post story detailing the alleged June 3, 1975, meeting between the woman's husband, Grimm and at least one other police officer.

A special prosecutor who is investigating Cowhig on misconduct charges is also investigating the incident.