LETTERMAN JOKER IN NBC DECK.(TV/Radio)

Byline: Steve Bornfeld

Yes, NBC drew to an inside straight when it held onto King Carson, and Jay Leno is showing signs of developing into a late-night ace.

But the wild card in this deck is still that disgruntled joker, David Letterman. And to hear NBC's head dealer tell it, this is one card that might have to be - reluctantly - discarded.

As reported on Sunday, NBC has signed "Tonight Show" legend Johnny Carson - at one time rumored to be talking to CBS - to an exclusive, multiyear deal to star in or produce prime-time specials.

The network also baggged Henry Winkler for a comedy series, John Candy for specials, director Barry Levinson as producer of a drama series and Dana Carvey, who agreed to a long-term deal that will include a series once his "Saturday Night Live" days are over.

But negotiations with Letterman, NBC's veteran late- nighter …