Three years ago, ''Stargate,'' a not-so-standard science-fiction action movie featuring Kurt Russell and James Spader, surprised everyone by earning more than $70 million. On the horizon, surely, was ''Stargate 2,'' if not 3 and 4. Instead, the movie's creators, Roland Emmerich and Dean Devlin, turned to a little project called ''Independence Day,'' and the ''Stargate'' enterprise was directed toward television.

That enterprise is now reappearing as ''Stargate SG-1,'' a weekly series on Showtime that will have its premiere tomorrow night at 8 in a two-hour special, ''Children of the Gods,'' then shift to its regular time slot next Friday night from 10 to 11.

''Stargate'' the movie won its large, eclectic following because it combined the adventure of space travel and military engagement with the mystery of intellectual detection. Mr. Spader played Dr. Daniel Jackson, a contemporary American Egyptologist who deciphered the symbols on an ancient stone wheel, rendering it active as a ''stargate,'' a portal to the far side of the universe. Mr. Russell was Col. Jack O'Neill, a cynical Air Force officer who then led a mission through this portal to a sandy distant planet where the Egyptian sun god, Ra (portrayed bizarrely by the androgynous Jaye Davidson), was alive and tormenting an enslaved people. Ra was vanquished, and the dreamy Dr. Jackson remained on the planet as his soldier buddies were funneled back to Earth and life as usual.

What of this challenging, if derivative, mix survives in ''Stargate SG-1''? More than a ''Stargate'' fan might expect but certainly less than one would hope for. The stargate itself, with its enticing curtain of shimmering light and its whiz-bang travel effects, is still there. In fact, it turns out there are stargates all over the universe, and other evil Egyptian deities to track down and to defend against. Gone, of course, are Mr. Russell and Mr. Spader, and both are missed, one more than the other.