Ex-College Football Star -- ALLEGED SERIAL RAPIST ... Arrested In Oklahoma

A former college football star -- who later became a police officer -- was arrested in Oklahoma City after officials say he's suspected of raping multiple women over the past 5 months ... while on duty.

The suspect is former Eastern Michigan linebacker Daniel Holtzclaw -- who dominated at EMU from 2005 to 2008 and later got a tryout with the Detroit Lions ... though he never made the squad.

After his football career fizzled, Holtzclaw became a cop with the Oklahoma City Police Dept. -- but he's behind bars on a $5 MILLION BOND.

Officials say the 27-year-old is accused of sexually assaulting at least 7 women -- all black and between the ages of 34 and 58 -- and that all of the incidents happened during his shifts while he was on duty.

Investigators say they've spoken with 6 of the alleged victims -- and are hoping to speak with the 7th as soon as possible. Officials anticipate there may be more victims.