By John Buckley

Simon and Schuster. 386 pp. $19.95

IF it's discovered that you broke some minor law when very young, or ran with the wrong crowd or perhaps clung to some pretty weird ideas, should it prevent you when older from becoming a Supreme Court justice, secretary of state or even a White House speechwriter?

That's the question John Buckley poses and attempts to answer in his sprightly political thriller about Tom O'Malley, a baby boomer turned White House speechwriter, whose dappled, if not quite shady, past lands him in the clutches of David Nicole, childhood friend, college roommate, Washington restaurateur, drug dealer, ex-felon and manipulative blackmailer.

O'Malley is to accompany the president on a swing through South and Central America. All Nicole wants O'Malley to do is smuggle 15 kilos of cocaine back to Washington aboard the presidential plane.

If he does, Nicole will forget that O'Malley sometimes acted as sales clerk for the thriving dope business Nicole ran out of their room at Amherst. If O'Malley refuses, then headlines will read something like: Ex-Dope Dealer Pens White House Speeches.

In tales of blackmail, the victim must decide which is worse -- the cost or the exposure. When the price demanded is only money, the choice is simple. Either the victim can afford it or he can't.

But when the blackmailer demands, as in this case, that the victim place himself in jeopardy that could land him a dozen years in some South American jail, the suddenly unsympathetic reader can be forgiven for urging the blackmail victim to forget all about the White House and go get himself another job.

Still, this same unsympathetic reader may never have spent much time in Washington, or even been absent for too many years and not know, or perhaps not remember, how proximity to power addles the brain. So there is a certain quirky logic when O'Malley agrees to smuggle the cocaine back through Andrews Air Force base where the White house staff luggage is rarely examined.

All this happens not now, but sometime in the future when an almost saintly Democrat is principal resident in the White House, whose inner workings Buckley describes in agreeable detail. He also presents Washington as if it were his hometown, which I suspect it is.

But there is much more between O'Malley and Nicole than blackmail. There is also the beautiful and engaging Kit Bowles, a former model and now an aide to a none-too-swift senator from Wyoming. Although Kit Bowles was once the lover of Nicole, the blackmailer, she has long since broken with him and is now beginning an affair with O'Malley, who apparently has loved her forever.

Meanwhile, the dim Wyoming senator is desperate for national attention. But instead of listening to Kit Bowles, he falls into the hands of what may be two of fiction's sleaziest political operatives. Their strange and wonderful machinations in behalf of the senator dovetail neatly into the novel's satisfying climax.

Others met along the way are a bibulous FBI agent who's running a full field clearance check on O'Malley; a nicely sinister mobster from Baltimore; and members of the White House staff, all suffering from various degrees of ambition and paranoia.

Of particular interest are O'Malley's parents: the father, a disgraced scourge that the CIA once loosed on hapless under-developed countries; the mother, a prosperous, if not quite rich, supporter of long-lost leftwing causes.

Buckley has written a likable, enjoyable tale and, without betraying its ending, which offers an almost guaranteed surprise, it's only proper to let him answer the question about whether there should be a statute of limitations on the youthful indiscretions of those now entering government service.

Here is John Buckley, speaking, I presume, through the voice of his protagonist, Tom O'Malley: "I'm part of a generation that can be blackmailed for having done something that was a natural part of being an adolescent in the nineteen-sixties and seventies . . . all of us, my age or nearabouts my age, when we go into government, we're expected to lie {about} having done things like smoke pot . . . I do think there should be some kind of amnesty, some kind of statute of limitations about drug use when you're attempting as an adult, to work in public service."

Arguments for exceptionalism are seldom compelling. Buckley might as well be asking the government to use common sense. But the special pleadings aside, he has written an entertaining and witty novel about the pitfalls that await baby boomers in Washington.

Ross Thomas's latest novel, "Twilight at Mac's Place," will be published this autumn.