Robert Chambers, bleary-eyed and unshaven after a night in the slammer, was arraigned on a crack-cocaine-possession charge yesterday in Manhattan Criminal Court. The notorious Preppy Killer — who was released from prison last year after serving 15 years for the 1986 Central Park murder of Jennifer Levin — ended up back in the clink Tuesday night after cops nabbed him in Harlem for driving with a suspended license. The crack-cocaine charge was added after cops found trace quantities of drugs in two straws and a tinfoil package spotted in his 1999 Saab, police said.