When Bill Cosby arrived in Washington yesterday he went looking for some soul food and found the entire city closed.

"This is the last time I'm coming to town on a holiday," he told a sellout crowd at Wolf Trap last night. "I couldn't get my fix. Have you ever tried to get halfsmokes at the Marriott?" The crowd roared and Cosby, dressed in a white jogging suit and seated n an armchair, was off and running for two hilarious hours.

One thing about Cosby; when a joke misfires you won't find him shrugging it off with some lame excuse like "you had to be there." He's too good a storyteller to leave his audience behind. Moreover, his current monologue is airtight.

The presidency, natural childbirth, health food, cocaine, gas pains, calves brains -- nothing escaped his gentle wrath or upset his timing measured by long pulls on a cigar.

But now it is his children, not his childhood, that fires his imagination and consumes his time on stage. He traced the lives of his teen-age daughters from birth to the present before confesing his newest concern; "I was worried that they'd be tracked down by boys much like myself," he confessed, "so I went out and bought a .357 magnum. . . two dogs . . ."

It is, as he says, the curse of parenthood.