Where's Jon? That's what fans of hip comic/actor/former talk-show host Jon Stewart have been wondering lately, nearly 15 months after CBS and David Letterman's Worldwide Pants production company signed Stewart to a wide-ranging development deal.

When the agreement was announced in June 1996, CBS and Worldwide Pants said Stewart would develop various prime-time projects for the network - including specials, sitcoms and, possibly, a late-night talk show which would follow CBS' Late Late Show with Tom Snyder, which is also produced by Worldwide Pants.

But despite the hoopla that surrounded Stewart's signing, the deal has yet to yield any concrete results, either on the air or off. Indeed, the funnyman's only formal connection with CBS since signing the deal has been appearing as a guest on Letterman's Late Show and filling in on Late Late Show when Snyder has been on vacation.

Industry sources say Stewart's relationship with CBS and Letterman is still on solid ground. The problem, according to those sources: Stewart is still deciding his next career move. "Jon really has to decide what he wants to do," one insider told The Post. "He had a budding feature career and a film deal with Miramax, and he may have wanted to focus on that for a while. It's a bit of a wait and see thing."

Worldwide Pants chief Rob Burnett, who's also the executive producer of Late Show, says Stewart remains a valued member of the Worldwide Pants family. "We've made a deal with Jon Stewart, and we think the world of him," Burnett said. "When the time is right for him and us, we'll try to think of the right project for him."

Sources say Stewart and Letterman have "bandied about" a few ideas for possible projects, but that so far, no single concept has clicked. Most TV insiders believe that the right project for Stewart will ultimately end up being a late-night talk show.

Stewart has impressed CBS execs the few times he's filled in for Snyder, with one network observer noting that Stewart has been able to easily segue from interviews with his comic friends to segments featuring politicians and newsmakers. "Jon's done well even though Snyder's one-on-one format is not really his format," the insider said.

Officially, both CBS and Stewart have said that any talk show hosted by Stewart would air at 1:30 a.m., after Snyder's Late Late Show. And in fact, CBS recently renewed Snyder's contract through the 1997-98 season.

"But looking to the future, we're going to be looking for something new in the 12:30 a.m. time slot - and eventually even the 11:30 p.m. time slot now occupied by Letterman," one top CBS source said, referring to a time perhaps five or more years from now, when Letterman could grow tired of the late-night grind. Letterman is currently under contract until 2002.

Indeed, some insiders speculate that one reason nothing has happened with Stewart and CBS yet is that Stewart isn't interested in doing a 1:30 a.m. show. So until Snyder steps down, Stewart's CBS career will stay on hold, these sources say.

As for Stewart's immediate plans, he just signed to star with comedian Janeane Garafolo in an upcoming romantic comedy for Touchstone Pictures. As for non-CBS TV projects, there's been talk that Stewart might replace Garry Shandling as the "host" of HBO's fictional Larry Sanders Show. Whatever happens, "Nobody here wants to lose Jon Stewart," one CBS insider said.