WHEN Tom Clancy published his first techno-thriller about a Soviet submarine and the American intelligence network, Pentagon officials said he must have had inside information to offer readers such precise descriptions of military tactics and technology.

The insurance salesman-turned best-selling author swore he got all his information from magazines and public sources, but many defense experts were not convinced.

Clear and Present Danger

By Tom Clancy

Putnam Books

656 pp., $21.95

This time around, though, few will challenge Clancy's claim that simple research and intuition give his books their uncanny sense of realism.

His latest effort, Clear and Present Danger, seems realistic not because of its description, but because of its plot--which anticipates with frightening accuracy exactly how the South American drug war has unfolded in recent months.

Government critics can't complain this time. That's something no one could have told Clancy, and it makes the book a worthwhile diversion for anyone with a few hours to spare.

CLANCY'S plot is straight out of today's headlines--maybe even a day ahead--as it weaves a story around a the federal government's efforts to fight the drug war.

First, Clancy shocks the reader with a brutal massacre of a family, committed by a ruthless pair of drug thugs somewhere in the Caribbean. Sound familiar?

A not-so-probable chain of events follows, making the incumbent Republican President more frustrated with his country's helplessness. Eventually he decides to conduct covert military operations against the Columbian kingpins. Sound more familiar?

Unfortunately, things go wrong, and word leaks out about the covert action. With the election months away, the administration panics and decides to cut its losses, covering up the operation and abandoning its para-military groups deep in the Columbian jungle. Sound really, really familiar?

EVEN the oblivious reader will notice the parallels Clancy draws to the Iran Contra affair--the book's bad guy is a carbon copy of John Poindexter, right down to rank and service.

But while the lack of subtlety is a bit insulting, it shows that Clancy's writing has matured since his earlier efforts.