(08-31) 04:00 PST Los Angeles — Fans of “The X-Files” have grown accustomed to season- ending cliff-hangers, but the biggest mystery now involves the future of the Fox network series beyond the coming season.

Although series star David Duchovny and creator and executive producer Chris Carter have indicated that this is probably the show’s final season, many observers figure that Fox wouldn’t want its most popular series to vanish from its prime-time schedule.

An already cloudy situation became cloudier two weeks ago when Duchovny sued 20th Century Fox Film Corp., which produces the drama, for breach of contract, alleging that the studio cut sweetheart syndication deals with its FX cable channel and other Fox-owned outlets rather than selling “X-Files” rerun packages on the open market. The suit contends that Duchovny, whose contract gives him part of the show’s profits, is thus deprived of his fair share of “The X-Files” bonanza, estimated to be in excess of $800 million.

The lawsuit’s most noteworthy detail, however, has an “X-Files”- like conspiratorial tinge to it: that Carter was in on the collusion and took “hush money” to remain quiet about Fox’s self-dealing. An aide to Carter declined comment.

Such an accusation might be expected to roil the waters as the series prepares to open its seventh season. But various sources deny that the show will be much affect ed by the lawsuit alone. Insiders say the future of “The X-Files” has a lot less to do with Duchovny’s grievance than with the costs of producing the show and the way business is done these days in giant media companies like Fox, which can control a series from production to broadcast to syndication.

Last season, “The X-Files,” which airs Sunday nights, was Fox’s highest-rated show, averaging 15.2 million viewers a week. As numerous as those fans might be, however, the price of producing the show — estimated at more than $3 million an episode, roughly twice what a typical network drama costs — is ultimately going to drive any decision about the show’s future.

For Fox, that could mean pulling the plug on its most popular show and thus weakening its own broadcast network, even though, a source acknowledged, “it’s awfully hard to let go of something that’s been so much a part of your net work identity, on your most important night.”

But, the source added, “this is going to be a cost-benefits scenario that gets played out over the next couple of months,” and the decision will be based on Fox’s wider corporate interests, not just what’s good for the network.

With a hit show, a studio usually passes along growing costs to the network by increasing the licensing fee. But because Fox Corp. owns the Fox network, that would mean passing along costs to itself.

A similar story played out last year when Disney, which owns ABC, decided that the enduring popularity of the network’s hit sitcom “Home Improvement” wasn’t worth the show’s rising production costs to the studio.

For Fox Corp., the cost of producing “The X-Files” increased considerably last year when Duchovny insisted that the show move from its base in Vancouver, British Columbia, to Los Angeles so he could be closer to his family. That meant giving up the tax breaks and lower labor costs afforded productions in Canada.

In addition, each episode of “The X-Files,” unlike other TV shows, is closer in scope to an independent movie, and executive producer Carter doesn’t have a reputation for cutting budgetary corners. One episode alone last season, which was set on a ship and featured flashbacks to the 1940s, cost more than $4 million to produce, an astronomical fee for a television series.

In conversations with the media, both Duchovny and Carter — who has another sci-fi series, “Harsh Realm,” premiering on Fox in the fall — have left the door open to continuing “The X-Files.”

“I wouldn’t say `never’ about anything, but as of right now, my contract is up at the end of this coming year, so I’m living my life as if this would be the last year, and I’d be fine if it were the last year,” Duchovny said at the recent summer gathering of television reporters in Pasadena.

Losing “The X-Files” would leave a large void in Fox’s Sunday lineup. There has been talk about continuing the program strictly as a series of movies, following the feature film released in 1998, and Duchovny has said he would be willing to remain part of the film series. A second film has been under discussion.

The question, however, remains: How well can two guys work together when one has accused the other of taking “hush money”?

“David still cares very much for Chris,” said a source close to the actor, adding that the two are writing an “X-Files” episode together. “This isn’t about Chris. He just happens to be involved peripherally.”