Jon Stewart will serve as guest host for CBS' Late Late Show With Tom Snyder Oct. 21-25, but everyone up the food chain at CBS insists this isn't Stewart's tryout as permanent host.

"Tom Snyder can do The Late Late Show as long as he wants to,'' David Letterman said through a spokesman Monday. It was the strongest show of support yet from Letterman, who clearly anticipated the inevitable speculation that Stewart is in line for Snyder's job.

Letterman's World Wide Pants production company produces Snyder and recently signed a deal to develop shows with Stewart. When the Stewart deal was signed, some late night TV observers speculated that the former MTV and syndicated talk show host eventually would inherit Snyder's 12:30 a.m. ET/PT gig. Stewart could challenge NBC's Conan O'Brien for young viewers and advertising dollars.

Letterman fanned the speculation when he confessed to Larry King earlier this year that there were questions about Snyder's performance.

But in a show of congeniality, Stewart was the guest on Snyder's show Friday night. The two joked like old pals. And Stewart says he's knee-deep in a deal to make films for Miramax, and any project with Letterman is still in the early talking stages.