TV stations are engaged in a high-stakes chess match that could determine the fate of the two biggest off-net comedies to come along in years.

The ultimate success or failure of Columbia TriStar TV Distribution’s “Seinfeld” and Buena Vista TV’s “Home Improvement” is being decided now in a series of secretive fall scheduling sessions.

Station execs are hesitant to set their schedules in stone, since they want the flexibility to counter-program the competition.

For the moment, however, the Tim Allen-Jerry Seinfeld slugfest is shaping up this way:

* In the top-ranked Gotham market, “Seinfeld” could threaten local O& O newscasts in its anticipated 11 p.m. slot on Tribune’s WPIX. (The only other top-10 stations believed to be looking at a latenight run for “Seinfeld” are a network affil in Dallas and an indie in Atlanta.) Fox-owned WNYW appears to be leaning toward 7:30 p.m. for “Home Improvement,” but sources say there remains a slight chance it could go at 7.

* It will be the battle of the titans in the No. 2 market, Los Angeles, with “Seinfeld” and “Home Improvement” anticipated to be gearing up for a head-to-head clash at 7:30 p.m. on Tribune’s KTLA and Fox’s KTTV, respectively. KTTV is expected to move “The Simpsons” back a half-hour to 7 p.m.

* The Fox-owned stations and affils in markets three to five (WFLD Chicago, WTXF Philadelphia and KTVU Oakland/San Francisco) intend to air the two megabits back-to-back in the access hour preceding primetime. It’s assumed that “Home” will land in the first half-hour; it’s a family comedy and would make a better transition vehicle from younger-skewing early fringe fare to access.

KTVU had been planning to double-run “Seinfeld,” but syndicator CTTD late last week rescinded the offer. Stations were unwilling to ante up the big bucks CTTD wanted for a second daily airing, which sources say would have equaled 50% of the license fee for the primary run.

The two runs would have enabled stations to use up all the episodes allotted them under the contract in a shorter period of time. Consequently, they could avoid the inevitable ratings fall-off after year three, according to Jack Fentress, VP-director of programming for the rep firm Petry National TV.

Double runs were never an issue with “Home Improvement,” which doesn’t have as much scheduling flexibility as “Seinfeld.” Most rep firms suggested that stations air “Home” in access, or at the very least toward the higher-rated end of early fringe, to recoup their huge investments.

“Seinfeld” plays to a sophisticated 18-49 audience, so stations would stand a good chance for success with it in either access or late fringe (loosely defined as the hour after primetime). That’s why a number of network affiliates in the top 50 markets, which are prohibited under existing regulations from showing off-net shows in access, have grabbed it.

Aside from KTVT Dallas, other big-market affils signed on for “Seinfeld” include WGPR Detroit (CBS), KPHO Phoenix (CBS), KCTV Kansas City (CBS), WSYX Columbus, Ohio (ABC) and WTKR Norfolk, Va. (CBS).

The Phoenix station is taking a unique approach to scheduling “Seinfeld.” Having recently shifted from indie status to CBS, it hasn’t had enough time to build a news operation. So KPHO intends to air a five-minute newscast at 10 p.m. following primetime, with “Seinfeld” bridging the gap into “The Late Show With David Letterman” at 10:35 p.m.

By the time stations set their fall skeds, most reps expect that “Seinfeld” will wind up with about 70% of its clearances in access.

In some instances, such as Los Angeles, station programmers are faced with making the same tough scheduling decisions that earlier faced web execs.

When the two shows squared off in their network runs on Wednesday, NBC was forced to move “Seinfeld” to Thursday, where it became a certified hit. Since then, however, “Seinfeld” has gone on to surpass “Home” in the ratings.

Although “Seinfeld” would likely attract a bigger audience at 7 than 7:30 in L.A., KTLA would have difficulty from an audience-flow standpoint if it were scheduled at 7. There, “Seinfeld” would come out of the younger-skewing “Full House” and “Family Matters,” moving into the slot where “Fresh Prince of Bel-Air” has prospered this past season. “Prince” looks like a better transition show than “Seinfeld” and would likely suffer at 7:30, with “Home Improvement” expected to bury most everything in its path.

The “Seinfeld” move by WPIX would buck conventional wisdom that it would air the expensive show in access.

Like KTLA, WPIX has incompatible family programming during those hours. WPIX currently runs “Fresh Prince” and “Family Matters” from 7 to 8, although it may plug similarly targeted “Blossom” – which just ended its NBC run – into one of those timeslots.

“He’s going to do very well,” says a buyer at J. Walter Thompson of Seinfeld’s 11 p.m. berth, predicting a 6 to 8 rating against O& O newscasts and “Jenny Jones,” but no other current sitcom competitors. An earlier slot “would be a problem because of the (audience) flow.” “Seinfeld” will likely bump “Cheers” to 11:30.

“I wouldn’t be concerned about it,” says Bud Carey, general manager at WCBS, whose late news is a distant third in the ratings. “The news audience is generally an older audience.”

Carey is hoping that “Seinfeld” in syndication will be less wildly popular than in its network run.