It's hard to tell which is worse in "Carbon Copy," the mawkishness or the jokes. Probably the jokes. The key one is that a white man who has suddenly found out he has a 17-year-old illegitimate black son goes for an angry walk on the beach, leaving footprints into which the son carefully steps. The father objects; the son asks whether a son isn't supposed to follow in his father's footsteps. Another joke is that when his luck runs out and he has to move to a cheap hotel, he's assigned to room 13 and the radio plays "Nobody Loves You When You're Down and Out." And that's just the comedy part. The part intended to be serious shows the hero, wearily played by George Segal -- he looks wearier with every long-suffering role in every insufferable comedy -- as the pampered victim of WASP America. Entering corporation land as a Jew with a black fiancee, he is easily led to change his name and exchange his fiancee for the boss' daughter. Slime though he has thus proved himself, we are supposed to believe that the Presbyterians with whom he has cast his lot are worse. His boss is ruthless, his wife is frigid and his step-daughter is spiteful. But as everyone in the film seems to agree that the only way to get ahead in the electronics business in California is to be white, Protestant and rigidly conventional in behavior and dress, and as the conditions include a company Rolls-Royce and membership in these people's golf club, the beneficiary is supposed to be seen as a victim, rather than an opportunist. No wonder, then, that he resents the intrusion of the black kid, who's bound to outdo him as a victim. Momentarily as snide as every other character in the film, the boy turns out to be perfect, having taken after his mother who, by all long-winded accounts in the film, was a saint. For 17 years, she waited, patiently and chastely, for her errant love to return, and then she capped it all by dying with forgiveness on her lips. One can only be glad she was spared, and wish that others could be as well. CARBON COPY -- At 14 area theaters.