By William F. Buckley Jr.

Random House. 264 pp. $19.95

William F. Buckley Jr., that paladin of the Right, is back with his ninth Blackford Oakes CIA novel -- and it just might be his last. Although "Tucker's Last Stand" differs significantly from the rest, it shares with even the wildest of these flashy entertainments a certain sense of authenticity drawn from the author's own service in the agency under Watergater Howard Hunt in Mexico during the '50s. (Surely more than a rumor!) Buckley knows his way around the CIA about as well as David Cornwell (John le Carre) knows MI5 -- which is to say very well indeed. But as we see Oakes in action, he seems to have far more in common with James Bond than with the tortured antiheroes who people le Carre's novels. Blackford Oakes may have difficulties, but he never doubts -- and as Buckley himself well knows, a thousand difficulties don't make a doubt.

How is "Tucker's Last Stand" different from the rest? Well, in the past, Buckley has never shirked from putting his man Oakes in the big picture. In general, the books are well researched. "Saving the Queen," which was about just that (though the one in question is the fictitious Queen Caroline I, not the real Queen Elizabeth II), got convincingly behind the scenes in Buckingham Palace; and in "Stained Glass," he conveyed the moil and welter of postwar German politics, and what's more gave us a bit of the 1952 American presidential election as a sideshow to the main action; and so on. But with his latest he attempts something more. "Tucker's Last Stand" presents his version of just how we got into Vietnam, and it is given to us through on-the-spot reports of Oakes's enterprise in Da Nang, Tucker Montana's work on the Ho Chi Minh Trail and in Saigon, a few swift scenes in Hanoi and a good deal of bold close-up reporting on the 1964 presidential campaign. Barry Goldwater, Lyndon Johnson and members of their respective retinues are characters. All this is done in quick-cut short scenes that create a sense of actuality and urgency.

What Buckley is up to here in "Tucker's Last Stand" is, in large measure, an effort to vindicate Goldwater. Goldwater was successfully framed by the Johnson camp as a dangerous kook, an extremist who would certainly involve America in a war, possibly even a nuclear war, if he were elected. Buckley provides Goldwater with a Deep Throat in the Pentagon (which he may or may not have had) who lets him know that it is Johnson's intention to commit the country to full-scale war in Vietnam once the election is behind him. Johnson -- crude, vengeful, a corn-pone Richard III -- is the best character in the book.

It was not, I think, intended this way. The title tells us it should be Tucker Montana. Buckley has provided him with a remarkable personal history -- the son of poor Mexican-American parents in San Antonio, a physics prodigy who was the youngest on Oppenheimer's staff at Los Alamos and actually flew on the Hiroshima mission to arm the bomb. Plagued by guilt for his part in it all, Tucker entered a monastery, then disappeared into the military as a kind of latter-day Lawrence of Arabia. All of this we are told. Some of it we are shown. But important turning points in his life are neglected, so that when Buckley offers Tucker to us as a tragic hero whose flaw is his great intelligence (or is it his guilt?), the man who could shut down the Ho Chi Minh Trail -- or open it up again -- we must take Buckley at his word.

And how does Blackford Oakes fit into all this? As colleague and comrade in arms. While Tucker is involved in his project, Blackford is busy creating the Tonkin Gulf incident, so that Johnson may get from Congress the blank-check resolution that he takes as empowerment to wage war. (You'll note a certain relevancy to recent events.)

As for the events in the book, historic and fictitious, Buckley does a good job convincing us it could have happened just this way. Goldwater, Johnson, Bill Baroody and Abe Fortas are all at least as convincing as Tucker and Blackford. And although "Tucker's Last Stand" should, perhaps, have been a bit longer and given more detail, the book in hand offers a fast ride to a strong ending and will waste no reader's time.

But we must consider that this one will conclude the series. On his way out of Vietnam, Blackford Oakes tells Rufus, his control, "I'm not against fighting apparently lost causes if there is at least the possibility of righting a wrong, of winning, but I don't see that there is, in Vietnam -- in this climate, in this way ... So -- it's time to go, after thirteen years."

Say it ain't so, Bill!

The reviewer is the author of several books, including the forthcoming mystery novel "Rough Cut."