BEVERLY HILLS, Calif. — There's something in the water, and in the air, and having spread through Hollywood, it's poised to invade your living room this fall.

Just as the Cold War fear of communism and nuclear annihilation in the 1950s sparked a surge in science-fiction films about alien invaders, the fear of terrorism looks to leave its stamp on the 2005-06 television season.

ABC, CBS and NBC all have new science-fiction dramas set for fall in which some heretofore unknown species comes into our midst, seeming to pose a threat to life as we know it. Each of these otherworldly life-forms emerges from the swamp or sea.

Part of the reason for this attack of the clones is the networks are all chasing the success of ABC's surreal post-plane crash serial "Lost," which proved there was a big audience for what had been seen as a niche genre.

But common ideas come from common experience.

"For my money, it's a reaction," said David Goyer, executive producer of CBS' "Threshold," which is about a covert government team established to respond to an alien contact that comes first out in the ocean. "There's a lot of anxiety in the world right now.

"What just recently happened in London and what's going on in Iraq and the West Bank, people are scared, and historically when people have been scared and people have been nervous, there's been an up-tick in science fantasy horror," Goyer said. "It happened in the '50s with the red scare and the space race and all of that, and there usually is a correlation."

Paranoia, said NBC Entertainment president Kevin Reilly, was a recurring topic of conversation with his development team going into this season.

"That was one of our themes," Reilly said. "These are paranoid times. Who's friend (and) who's foe? What's in our interest in national security? That was definitely on our mind. ... You don't want to literally go at those themes, because they make you uncomfortable. You want to kind of bring them out and manifest them in other ways, give us a way to work them out."

The makers of NBC's "Surface," which has mysterious creatures emerging from the sea, and ABC's "Invasion," where residents of a small Everglades town are infiltrated after a devastating hurricane, are coy about whether their respective interlopers are extraterrestrials. But there's no mistaking their impact — or inspiration.

"We're living in an aftermath world," said "Invasion" creator and executive producer Shaun Cassidy, the 1970s teen idol. "When I was a kid, the big scary monster was, 'The bomb's going to come, and that's going to be the end,' and the bomb didn't come. Very, very, very, very terrible tragedies have come, and there hasn't been a rule book for the aftermath, trying to figure out what to do next, trying to find our way, trying to put the pieces together in a more productive way. Those are the themes of our show."

Just as Steven Spielberg's recently released film "War of the Worlds" was informed by the attacks of 9/11 and all that's happened since, so too in their own way are "Threshold," "Surface" and "Invasion." Unlike "Over There," a new FX cable drama about the Iraq War, these shows reflect current situations more obliquely.

The shows may owe a debt to natural disasters and other dangers as much as to terrorism, but the big boost came from "Lost," which showed viewers had an appetite for shows that left unanswered questions at the end of each episode.