By Tom De Haven
Updated November 18, 1994 at 05:00 AM EST

Kill me, but for a long time I had Dean Koontz figured for a bush-league Stephen King. That was before I actually read some of his novels (Cold Fire, The Bad Place, Watchers) and realized just how wrong I’d been. His imagination isn’t like Uncle Stevie’s at all — it’s not even close. It’s way scarier. In Koontz, Big Science, not some toothy bogeyman, is the plot’s stuff of nightmares and a legitimate cause for paranoia. ”We’re living in a time when the highest of high technology makes it possible for a relative handful of totalitarians to subvert a democratic society,” writes Koontz, clearly a troubled citizen, in DARK RIVERS OF THE HEART (Knopf, $24). Fortunately for us, he’s turned his deep political apprehensions into a humdinger of a chase novel.

Cooped up in a small cabin with only his skittish dog for company, ex-cop Spencer Grant (not his real name, as we learn later) is living like one of William Gibson’s cyberspace cowboys. His days are spent hunched over a computer, deleting all traces of his existence from databases. As with so many of Koontz’s heroes, though, Grant is a loner — an invisible man — not entirely by choice.

Grant then meets and falls in love with Valerie Keene, who suddenly vanishes without a trace. Searching for clues at her house, he is nearly killed by an assault team that bursts in on him, and is forced, like Valerie, to go on the run — the target of a government agency that does not officially exist, a neo-fascist cabal ”under the control of the Justice Department.”

Koontz creates, for its chief assassin, a genial madman guaranteed to give you the creeps. Pudgy Roy Miro, with his ”twinkly blue eyes and warm smile,” envisions himself the Good Samaritan of the ”brave new world order.” His ultimate goal is to eliminate — with compassion, of course — 90 percent of the U.S. population and create a perfect society.

With Miro and his paramilitary corps in hot pursuit, Grant eventually hooks up with Valerie again. As they flee from Nevada to Utah to Colorado, the novel explodes with all the giddy excitement of a half-dozen James Cameron pictures.

Dark Rivers of the Heart (a lousy title for such a superb thriller) deserves to go to No. 1 on the best-seller list. And to bump — why not? — Insomnia down a notch or two. A