Summertime and the Reading Is Easy : A Good Paranoid : Just when you thought it was safe to go back to the office . . . : VERTICAL RUN. <i> By Joseph R. Garber (Bantam Books: $21.95; 305 pp.)</i>

Joseph R. Garber’s relentless thriller “Vertical Run” takes the second word of its title quite literally, providing all the breathless pace and heart-pounding action one could wish while lounging ocean- or poolside. It also offers one added lure for readers lazing in the sun--the suggestion that going back to work may be hazardous to your health.

Garber’s hero, Dave Elliot, is the sort of dedicated executive who rises at 5:45 a.m. to get an early start on the job. His set routine has him jogging along Sutton Place, arriving at his 45th floor Manhattan office suite by 7. After a bracing shower, conservatively dressed in a lightweight tan suit and feeling like a million, he steps into his office to find his normally genial boss inexplicably pointing a gun at him, finger tightening on the trigger. He dodges that bullet only to have an even deadlier encounter in the company’s reception area with a complete stranger named Ransome.

Once again he escapes, but he’s still 45 floors away from safety. Trusted friends and associates turn against him. His own family sides with Ransome. And as the building continues to fill with code-named hard-cases wielding cutting-edge weaponry, poor Dave discovers firsthand what everybody who has seen the film “Die Hard” knows full well: that trying to exit a skyscraper under those conditions can be quite a daunting task.

Fortunately, our hero is as difficult to dispatch as, well, the hero of “Die Hard.” As the bodies of the bad guys (or are they good guys?) pile up, so do questions about what’s going on here. Why is Dave Elliot at the top of everybody’s hit list? How is he able to dispose of so many of his enemies so efficiently? Has he gone mad, as Ransome suggests? Is Ransome really working for a government agency? Elliot can’t make heads or tails of his living nightmare and neither can we, which is as it should be. Confusion is the stuff suspense novels are made of, especially those sub-categorized as “paranoids,” of which this is a prime example.

Garber, a business analyst and columnist for Forbes, uses a writing style that can best be described as economic. His prose is lean. His cast is minimal--protagonist, antagonist and nominal love interest, along with an assortment of secondary characters who are lucky to get more than a line or two of dialogue. But one is left with an impression of efficiency rather than inadequacy. And he doesn’t skimp when it comes to rounding out the dimensions of his main players.

Elliot, in fact, has more time center stage than Shakespeare gave Hamlet. But, unlike the melancholy Dane, he isn’t allowed the luxury of speaking directly to the audience. Maybe Garber wanted to keep some of Elliot’s thoughts a mystery. Whatever the reason, the novel is not told in the first-person. How is the reader to know what the hero is mulling over, since he’s alone throughout much of the book? In trying to solve this problem, Garber makes his only false step. He provides Elliot with an alter ego who converses with him in italics, tossing out cautionary quotes, such as: “He who overcomes his enemies by stratagem, is as much to be praised as he who overcomes them by force. Machiavelli said that.” In some instances, though, the alter ego is stating the obvious: “If you try to show anyone the proof of what happened, they’ll just shake their heads. Poor old Dave, they’ll say, it’s all in his mind.”

Happily, not even a know-it-all, Machiavelli-quoting inner voice can slow the pace of this engrossing novel. From the moment poor old Dave begins his run until the epilogue that gives his story a surprising 180-degree twist, this is a piece of suspense fiction that’s designed to be devoured in one or two sittings. If you’re taking it to the beach, use plenty of sun block.

“Vertical Run” is also available (abridged) on four audiocassettes from Bantam ($21.95).