THE FOURTH PROTOCOL Michael Caine, Pierce Brosnan. Directed by John MacKenzie. 1987. R (Lorimar, stereo, 119 min., $89.95)

Frederick Forsyth, who wrote both the novel and the screenplay of "The Fourth Protocol," admits this was a difficult story to bring to the screen. We've got a British spy (Caine) vs. a Russian (Brosnan) who, because of internal Soviet political struggle, has been directed to plant and set off a bomb near an American air base in England. What we've really got, then, is a twisting and turning mind puzzle. Frankly, that's one rason why it works much better on home video than in a theater.

This is solid, intelligent movie, well paced and intriguing. Unlike so many other thrillers, it does not underestimate us or pander to the lowest common denominator as it presents its complicated and perhaps all-too-real spy story.

Caine, who turns in a terrific performance, is matched by the surprisingly good Brosnan (of TV's "Remington Steele" and the upcoming "Noble House" miniseries). With little dialogue, Brosnan is magnetic, handsome and hateful.

For those of us who don't quite catch all the important innuendos and key plot devices the first time 'round, what a pleasure to be able to stop the cassette, rewind and pick up what we missed. In the privacy of our own homes, we can admit that maybe we're not quite as smart as the movie.

And this is one movie in which you won't want to miss any detail. Totalling up those details makes this one a real corker.