A couple of captains, trekking together boldy going where no plot has gone before.

It is a momentous sight. When, in Star Trek Generations, Capt. Picard implores the venerable Capt. Kirk to help fight an alien force, this time- defying moment has the impact of Bill Clinton summoning Woodrow Wilson to save America from the Klingons.

 On big screen or small, Star Trek has a gravitational force that reliably pulls in the audience. The movies and TV shows reassure us that there will be a future, and that it will be fun if we don't mind a couple of pesky Klingons in the passing lane.

 Although Star Trek Generations, the seventh in the immensely popular film franchise, can boast some renegade Klingons, and blends some from the original Trek with those from TV's The New Generation, mostly it's a slow, intergalactic voyage to The Twilight Zone.

 That the new picture teams the original Enterprise's Capt. Kirk (William Shatner), with latter-day skipper Picard (Patrick Stewart) is some neat trick, as the two men live approximately a century apart. But a film franchise, even one as dependable as a fast-food outlet's, has to have a gimmick.

 Kirk and Picard reach across time to block archvillain Dr. Soran (Malcolm McDowell) from hijacking the solar system and plunging it into the Nexus, a ''temporal flux. ' In plain English, Nexus is a time warp that in this context might better be dubbed a generations gap. But does it take two captains to save the universe from a shampoo?

 Time is the essence of Generations. It is twisted like a pretzel so Kirk and Picard can join forces. It is a warp that creates turbulence for starships and their passengers, who pop off the walls like corn kernels in a microwave. It is cheated by the veteran Enterprise officers who get a chance for eternal life. It is reconsidered by Data, the Tin Man-like android, who gets an emotion-chip implant and gets the jokes that have eluded him for the last seven seasons of Star Trek : The Next Generation.

 Time is of the essence but, alas, it is also squandered in this overlong, overplotted film that elapses in three parallel but overlapping time/space continuums. This geometric impossibility proves narratively impossible as well.

 Wearing more hair than they were biologically blessed with and looking as though they have been preserved in formaldehyde, Kirk appears along with Scotty (James Doohan) and Chekov (Walter Koenig) in the first continuum. Here, some on the Enterprise get hijacked to Nexus, the second continuum, a nirvanalike place where "time has no meaning," and where visitors are in suspended animation, doomed to relive their favorite moments. Like the real Abraham Lincoln sentenced to an afterlife as a permanent boarder in Disney World's Hall of Presidents.

 Seventy-eight years after Enterprisers are marooned there, Capt. Picard crashes on Nexus, discovers Kirk, and enlists his help in fighting Soran, who wants Nexus to suck up most galactic civilizations.

 Once the two captains finally meet up, the film finally gathers some momentum - and becomes an old-fashioned western. The youngish cowboy, Picard, begs the old saddlehand, Kirk, to come out of retirement and clean up Dodge - excuse me - the galaxy. For Picard, it's a moral imperative. For Kirk it ''sounds like fun. " As Kirk, Shatner is so good in this sequence it's a shame he isn't around to lend the entire movie his offbeat humor and enthusiasm.

 A Star Trek film, or episode, is only as good as its villain. Sadly, in Generations the nefarious Soran is so ill-defined, his plot to reconfigure the galaxy and send it into the Nexus limbo so abstract, it's hard to understand why Picard's forehead has furrows deeper than a Klingon's.

 Three things make the film worthwhile: Shatner's performance; the sequence involving Data getting his "emotion chip" implant; and John Alonzo's crystalline cinematography, which makes Generations the most beautiful Trek ever.

 Finally, the moral of Generations is that Enterprise captains may come and go, but Star Trek is eternal. You, and Paramount Pictures, can take that to the bank.