DAVID FROST may be the missing link - not between humans and the lower apes, though let's not rule that out - but between journalism and show business. Frost was a pioneer in merging the two - the pursuit of reality and the escape from it - on his old syndicated interview show. His British accent and a pseudo-incisive questioning style gave him an illusory reportorial legitimacy,) but we knew what he was really after - the showbiz ham in every public figure and the "marvelous quote, to borrow one of his most overused pharses, that would serve as an ornamental surrogate for that much-avoided television taboo, substance.

Substance can be so boring.

And so Frost broke ground on which later would dance the likes of Tom Snyder, Phil Donahue, producers of innumerable "docu-dramas," bubbly-bright local news personalities in city after city, and anybody else who could master the new video art of turning information into something as attractive and meaningless as "Charlie's Angels."

Mike Nichols and Elaine May once satirized the trivializing aspects of sycophancy disguised as reportage in a classic routine about a small-town disc jockey who sprays-mists his conversation with such dropped names as "Al Schweitzer. This idea, that all celebrities can be rendered equal through equal media exposure, isn't even a baby-step from the mentality and operating procedure of a David Frost, who always liked to have his political or topical guest perform their "marvelous quotes" the way Sammy Davis Jr. might perform "My Way."

It is no surprise then that "I Gave Them a Sword" - Behind the Scenes of the Nixon Interviews, Frost expresses symptomatic admiration for "the quotes of the Nixon era" as if they were Henny Youngman one-liners and the era itself something staged for the world's amusement. Frost is an arch popularizer of the miuse of "quote," but the remark is significant beyond its personification of Frost's laissez-faire syntax. The Nixon years were entertaining - well, yes, and Dresden must have been photogenic - and in pursuing Nixon for a television confessional, Frost undoubtedly saw a glitzy, boffo, jolly good show as the real goal.

He only got one good show, however - the Watergate show - and Frost's book seems largely an attempt to rewrite history by pronouncing the entire series a smashing success and pronouncing the entire series a smashing success and rescuing from the cutting room floor new tidbits of chatter about that fascinating charlatan who became the 37th President of the United States. There are some savory asides, like the morning before a taping when Nixon casually asks if Frost had done any "fornicating" over the weekend, but essentially the book fits in with Frost's career effort to bring life's marginalia in from the margins and to place the peripheral on a pedestal. Insights into the Nixon mystique are generally of this caliber: "A sad man, who so wanted to be great."

Many balked at the thought of Frost being the one to interrogate Nixon after his exodus from the White House, but it really turned out to be an apt match, in a macabre sort of way. Here were two television professionals meeting face to face to see not who could out-fox the other but who could best exploit his own mastery of the medium. It was also to some extent a contest of grotesquerie; on the air, Frost's pasty puss looked like Nixon's with the air let out of it.

Frost insists early on that he went into as "a deadly serious journalistic project" and surrounded himself with "first-rate journalists," implying that he is one, too. His research team may have been exemplary, but the man wielding the research is to journalism what Sidney Shelton is to literature. At least Sheldon doesn't proclaim himself a Tolstoy.

Frost doesn't seem to see a whisper of conflict in the fact that at the same time he was girding himself for the task of interrogating the wily Nixon, he was also occupied with signing up stations to carry the telecasts, arranging for ample press coverage from Time, TV Guide and other carefully chosen periodicals, scrounging up the loot to pay Nixon, and wooing such sponsors as Radio Shack and Weed Eater to buy ads that would make the shows profitable.

All these negotiations take up many pages (only when it gets time to hand Nixon a $200,000 check is the narrative very compelling, and quite funny besides) and include among other curious details conspicous mentions of the restaurants in which preliminary talks took place: 21 and Trader Vic's in New York; Rive Gauche in Washington; L'Escoffier and Chasen's in Los Angeles. We are also informed that Frost rented a Mercedes 450 to commute from L.A. to San Clemente. Ah, the life of a reporter!

The actual interviews are recounted at some length and include material excised from the TV tapes and restored for the book. Frost unfortunately fingd it necessary to take us aside now and then to remind us what a bang-up job he's doing in penetrating Nixon's defenses: "I was pressing on . . . " with the grilling; Nixon was "a man in pain" under Frost's lash, "Encouraged by my success . . . " Frost pludged ever deeper until Nixon was "thoroughly beaten." One almost begins to pity the scoundrel making the fortune from the ordeal - Nixon, that is.

Frost's writing style is faithful to his television demeanor. There are no fewer than 50 separate uses of the word "indeed" in the book's eleven chapters and epilouue, plus generous spinklings of "in fact." These random-emphatic buzzies are there to give the impression that Frost is really leveling, really hitting the old nails on their old heads. But it's all part of his shrewd TV savvy; bamboozle the customers with external decoration and assume they'll be too entertained to bother demanding anything so drab as ungimmicked actuality.

None of this is meant to suggest that the Frost-Nixon interviews were any kind of gross outrage; to a certain extent they were fun - maybe grisly fun at spots - and by this time it's hard to work up much dudgeon, high or low, about the checkbook-yournalism aspects of the deal. Because it wasn't journalism anyway, was it? - after all indeed, in fact or in deed. It was show business, with all the accepted trappings, from lunch at 21 to the Mercedes 450 to Nixon's agent Swifty Lazar to Frost's frantic telephone calls to secure backers.

The distressing thing about Frost's book is that he doesn't seem to recognize any of the obvious attendant ironies of the whole affair; he keeps insisting on the whole affair; he keeps insisting on the integrity of his journalistic soul even while Weed Eater is on hold and his foreign bankers are balking. Also, though negotiations between Frost and Nixon and Frost and the rest of the world are fairly thoroughly detailed, there is one aspect of the operation conspicuously absent: Frost's negotiations for a book contract to write "I Gave Them a Sword."

Maybe that's because "Frostie," as he apparently doesn't mind being called. is saving that juicy matter for yet another book - "Behing the Scenes Behing the Scenes of the Nixon Interview." Don't say it wouldn't sell. These days, don't say anything might not sell.