BOOK REVIEW : In Search of a Carefree Kerouac Summer : ALL SUMMER LONG <i> by Bob Greene</i> Doubleday; $23, 389 pages

“On the Road” it isn’t. This is Kerouac with a credit card, a rental car, a parturient paunch and a penchant for afternoon naps.

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This is about three middle-aged men who take the summer off to bum around, and it is absolutely captivating--a funky hosanna to lasting friendships, small towns and dog days.

To everyone but Ben Kroeger it’s a preposterous notion. Ben, a generic network correspondent, is back in Bristol, Ohio, for the 25th reunion of his high school class. A reunion, he notes, “is supposed to be a reminder of better times. It’s not supposed to be a promise of anything. It’s like a taunt. ‘This is what you used to have.’ ”

What Ben--what all of us--used to have is summer. Summer lasts forever to the young, an enchanted time interrupted only by nine months of school. To an adult, whatever that is, it’s just another season. The warm one.

To his two best school friends, Ben proposes “one more summer in the sun.” Just pick up and go. No timetable. No particular destination. Total irresponsibility. “A gift to ourselves.”

It’s the odd couple plus one, a trio of 43-year-olds born to bounce lines off each other. Ben is semi- famous (“Don’t I know you from somewhere?”). Ronnie has become a tycoon-by-marriage, given to Cuban stogies and the country-club-locker-room growl of the prosperous. Michael still lives in Bristol, an 11th-grade teacher, a man of preternatural kindness, happily married, beloved by all, harboring an unspoken resentment: Why are all my classmates prosperous, renowned or both?

Their first miles are moist with Pavlovian urges to consult watches, make schedules, eat when they “should” instead of when they’re hungry. But within days endemic tensions have peeled away. We know we’re finally in summerland when narrator Ben realizes with glee, “I don’t think we’ve said one important thing all evening.”

Idle tongues, though, make the best company; idle eyes are the best observers; idle brains spin the sweetest memories. While the three amigos drift from Omaha to Cape Cod, New York, Florida, California, fresh observations cozy up to nostalgia in an all-American pastiche ranging from catching fireflies and the smell and ping of pebbles on newly laid blacktop, to the invasion of the camcorder (“not capturers of memories; substitutes for memories . . . Nothing that happens when the camera is turned off is considered to have really occurred.”)

While the trip will change each man’s life--subtly at first, then dramatically--in the hands of author Bob Greene it is a romp-and-a-half.

When not contemplating poolside moms or consuming prodigious quantities of ribs, Ben, Michael and Ronnie find themselves in places like the (locker room of the Chicago Cubs. (When two of their baseball idols emerge from the showers, the vacationers are privy to their immortal words, “ . . . Sudafed, I think. If that makes you tired try Actifed.” They end up in the Elvis Suite at the Mirage in Las Vegas, complete with the King’s white baby grand and the sobering reminder of William Carlos Williams: “The pure products of America go crazy.”

On a less lofty plane, we are left to ponder Ronnie’s assertion that “the best place in America to meet women is at a Chuck E. Cheese’s” and Ben’s contention that “you should never live in any town that doesn’t have a Main Street.”

It is oxymoronic to suggest that the unexpected happens to a trio that expects nothing. Nevertheless, Greene, a syndicated columnist for the Chicago Tribune and master of the mot, drops drama into his thoroughly engaging tale in just the right dosage. A zaftig dental hygienist joins the road show for a spell; an old girlfriend shows up in Dallas, kids in tow; one of the men loses his job; one quits . . . Fittingly, the ending is not tidy-- life is not tidy--but it is satisfying all the same in this quintessential summer book.

Just one question. Whatever became of fireflies?