SANTA CLARA, Calif., Dec. 29 (AP) -- A man headed for a liquor store was unharmed by a commuter train that ran over him Thursday afternoon as he huddled in the middle of the track, between the rails. The 35-year-old man, Anselmo Castillo Campos, was arrested on a charge of public dunkenness after his brush with the three-car CalTrain commuter express which was going 20 miles an hour. The train, on its way to San Francisco, was delayed 25 minutes while paramedics and polic officers examined Mr. Campos, who smiled and waved to bystanders.