CESSNA 210, N212FS, WAS CRUISING NE ON AN IFR CLNC AT 7000', SQUAWKING A DISCRETE TRANSPONDER CODE, WHILE CESSNA 172, N19649, WAS CONVERGING HEAD-ON, SQUAWKING 1200 (VFR CODE). THE 210'S GND SPD WAS 174 KTS; THE 172'S GND SPD WAS 138 KTS.THE ATC CTLR ADZD THE 210 PLT THAT THERE WAS 'TRAFFIC 12 O'CLOCK, 5 MILES, OPPOSITE DIRECTION, ALTITUDE UNKNOWN.' THE 210 PLT ACKNOWLEDGED, BUT NEITHER HE NOR HIS PAX SAW THE CONFLICTING TRAFFIC UNTIL MOMENTS BEFORE IMPACT (NEAR A VOR STN). HE INITIATED EVASIVE ACTION, BUT HE DID NOT BELIEVE THERE WAS SUFFICIENT TIME FOR THE ACFT TO RESPOND TO CTL INPUTS. DRG IMPACT, THE LEFT WINGS OF BOTH ACFT WERE DMGD. THE 210 CONTD FLYING & WAS SUCCESSFULLY LANDED, BUT THE 172 WENT OUT OF CTL & CRASHED. THE 210 PLT ESTIMATED THE VISIBILITY WAS AT LEAST 50 MILES. VISIBILITY AT THE NEAREST WX STN WAS RPRTD TO BE 40 MILES. THERE WAS NO RADIO CTC WITH THE 172. THE 210 PLT DID NOT USE HIS LNDG LIGHT & THERE WAS NO INDCN THAT THE 172 PLT HAD USED HIS LNDG LIGHT, NOR WAS THE USE OF A LNDG LIGHT REQUIRED.