Edward Thomas Mann, the former IBM employe accused of killing three men and wounding six others during a shooting spree in an IBM office building in Bethesda last month, was indicted yesterday by a Montgomery County grand jury on 75 counts of murder, assault and illegal use of a handgun.

According to court papers, Mann was indicted on charges of murder, assault with intent to murder and use of a handgun to commit a crime of violence in connection with the deaths of Hung Phi Nguyen, Larry Lewis Thompson and Jesse Robert Lewis.

The remaining 69 counts consisted of attempted murder, assault with intent to murder and illegal handgun use in connection with 23 other persons listed as victims in the incident, according to court papers.

Mann, 38, of Mitchellville, is being held without bond at the Montgomery County Detention Center. He is to face the indictments in a Montgomery County Circuit Court hearing today, court officials said.

On May 28, Mann, a marketing representative who worked for IBM for 13 years, rammed his Lincoln Continental through glass doors at the IBM building off Democracy Boulevard, near Montgomery Mall.

Armed with several automatic weapons, Mann fired 150 gunshots throughout the three-story building during his 7 1/2-hour siege.

A discrimination suit Mann filed against IBM in 1977 was dismissed by the D.C. Human Rights Commission for "no probable cause."