The jury is still out on what a guest spot actually does for a supporting actor's career. ''The credit hasn't superseded Broadway in terms of casting, but it's allowed all of us who work in the business to see actors we might not have seen otherwise,'' said Tara Rubin, a casting director for ''Mama Mia!'' and ''The Producers.''

But the parts these actors are playing might not be the ones they want casting directors to see. ''I don't feel like a lawyer, but they always cast me as a lawyer,'' said Bob LuPone, who has appeared in six episodes. ''It hasn't done anything for my career to bring me out of the fray, as it were, as a career actor.''

Nor has Mr. Walker been able to turn his appearances into a career that lifts him out of his SoHo coffee bar. So far, he has made $15,000 to $20,000 for three guest spots on the ''Law & Order'' shows, but has yet to find an agent. ''They can't figure out my type,'' he said, referring to Manhattan agents and casting directors. ''I get a lot of 'downtown hipster guy.' I mean, what does that mean?''

So Mr. Walker auditions mostly for commercials, like one for a beer. ''It was a party scene,'' he said. ''They hired a hypnotist, and the hypnotist says to one of the guys, 'You are a dog.' '' Then another guest appears with beer. Everyone runs over to him, and the scene shifts to the hypnotized guest lapping water out of the toilet bowl -- '' 'cause he's still a dog,'' Mr. Walker explained grimly. ''And they wanted me to play the dog.''

On the other hand, John Dossett, who is starring in ''Gypsy'' on Broadway, recalled that last year he missed an audition for ''Dinner at Eight'' at Lincoln Center but was cast anyway from a ''Law & Order'' tape.

Casting directors on the ''Law & Order'' shows maintain they now have a difficult time finding new faces -- which might be the first time in the history of the New York acting world that demand has outstripped supply. Last season, Mr. Wolf ordered directors to wait 60 days between casting the same actor twice in prominent guest roles on any of the three shows. ''We don't want someone to tune in Wednesday night for 'Law & Order' and then Sunday night for 'Criminal Intent' and see the same actor playing the villain in one show and the cop in the other,'' said Gayle Keller, the casting director of ''Criminal Intent.''