'MASH' Star William Christopher Death Certificate

"MASH" star William Christopher -- who played Father John Mulcahy -- died from cardiorespiratory arrest ... this according to his death certificate obtained by TMZ.

The document also lists small cell carcinoma as a contributing factor, something we're told was non-lung related. Christopher died on New Year's Eve in his Pasadena home at 7:12 AM.

The death certificate also notes he was in the entertainment industry for 60 years.