ABC calls "The French Atlantic Affair," which starts tonight at 9 on Channel 7, a "six-hour suspense thriller." Even if it were possible to maintain thrilling suspense for six hours, who would want to be thrilled and suspended to that extent?

As it happens, six minutes of tension would be a better estimate of this pleasantly preposterous but hopelessly prolonged picture -- at least judging by tonight's two-hour opener. Remaining episodes will be shown Friday and Sunday at 9 p.m.

Based on a novel by Ernest Lehman, "Affair" fantasizes an ocean liner hijacked by the fanatical leader of a kook religious cult. The cultists take over the French-Atlantic Line's good ship Festivale and threaten to blow her up unless they get a plane load of gold ingots and safe passage to a promised land they have promised themselves.

To give you an indication of how vile these dastardly loonies are, they not only stab a jolly fat French crewman, they take a Polaroid picture of his corpse as well.

The film is colorless and dim, barely opaque, but it does offer a blank wall against which bored actors can do some fey tomfollery. It's high ham on the low seas when Telly Savalas, as the cult leader, strides into the captain's quarters with what looks like a Cartier frying pan around his neck and snarls in his best James J. Kilpatrick manner, "Captain, your precious ship is a split in the ocean compared to the power of the Cosmic Path."

His followers are searching for "a life closer to duh truth," Savalas tells Louis Jordan who, as the captain, never has to leave his cabin and barely has to stand up. This is one of those all-star productions in which the bigger the star, the smaller the role. Hence there is a lot of Chad Everett as a journalist who hates the cult and little of Shelley Winters as the gang's reigning yenta.

Whether America is in the mood right now for a movie in which hostages are threatened with death is questionable, but "Affair" is so far removed from any port in the storm that this probably won't matter. The producers of "The Love Boat" had a heavy hand in the film, which shows; it was both written and directed by Douglas Heyes, who has managed the trick of constructing a movie-by-committee all by himself.