A federal grand jury yesterday accused a former District of Columbia police officer of conspiring to steal goods from a huge military exchange system warehouse in Ohio where he was head of security and sell them to Northern Virginia residents, including employes of Koons Ford in Falls Church.

The seven-count indictment, returned in Alexandria, said the items, including video tape recorders, cameras and pen and pencil sets, were valued at at least $18,600 and were sold to Koons employes and others at well below the marked prices.

Charged in the indictment with conspiracy, interstate transportation of stolen goods and receiving proceeds from the sale of the items was Robert Harvey Strain of Dayton. A law enforcement source said yesterday Strain left the District police force in 1975 after 12 years. Strain could not be reached for comment.

Last Friday, Toivo Emil Ekroos, a new car salesman who left Koons Ford in August, pleaded guilty in U.S. District Court to a single conspiracy count in connection with the case. Ekroos and Strain met, the source said, while Ekroos was working as a salesman.

Ekroos, 42, of Sterling, Va., declined comment, except to say, "I didn't know what was going on on the other end of this thing. I knew something was going on, but I didn't know what."

Spokesman Al Hein of the FBI's Alexandria field office said yesterday officials of the Army and Air Force Exchange Service, located at Wright-Patterson Air Force Base in Dayton, are "very concerned about the way the losses occurred -- the apparent ease" with which the goods allegedly were stolen.

A U.S. task force based in Dallas and including federal prosecutors and FBI and Internal Revenue Service agents has been investigating alleged bribery and corruption in the exchange system nationwide for the last 4 1/2 years, a congressional investigator said. The probe has centered, he said, on the exchange service's headquarters in Dallas, where 75 percent of its procurement is done. He said 85 firms or individuals have been barred or suspended and 22 others subjected to some judicial action since the investigation began.

Yesterday's indictment accuses Strain of making five trips from Dayton to Northern Virginia with stolen merchandise between April and September of this year.