The amateur's amateur writes a real, live novel

SIDD FINCH has learned to throw a baseball at 168 miles per hour. His speed and deadly accuracy are threatening the entire game of American baseball. ``When I wrote the story in 1985 for Sports Illustrated as an April Fools' joke, the magazine got more letters than any feature ever - including their bathing suit issue,'' says author George Plimpton. The St. Petersburg Times even sent a television crew to the Mets training camp to try to film the fictitious Finch during practice. ``Of course they never found him, but the Mets never let on that he never existed. They were in on the whole hoax.''

Out of that story, and the resulting furor, interest, controversy, and promise of reader demand comes the full chronicle (``The Curious Case Of Sidd Finch,'' New York: Macmillan, 275 pp. $14.95). ``This guy can change the face of the future,'' says one Mets scout in the novel, after watching Finch wind up and decimate bottles perched atop a distant fence.

The story begins as the narrator is called to the Mets' spring training where catchers are readying themselves for Finch fastballs by having baseballs lobbed to them from a blimp 8,000 feet in the air. It is the first novel from Mr. Plimpton, the amateur sportsman who tried his hand at professional football (``Paper Lion''), golf (``Bogey Man''), hockey (``Open Net'') and then wrote about his exploits. He is also longtime editor of the literary quarterly, The Paris Review.

``I thought it was going to be fun to not have to tell the truth, you know, to lie, which I think all novelists of course do - and not have to be accurate,'' says the lanky Plimpton, sporting shaggy gray hair, beneficent smile, and the familiar, basset-hound eyes. He sports a 1969 World Championship Celtics wristwatch - the season he donned a Celtics' uniform - complete with green shamrock face and basketballs for the numerals.

``But having to lie turned out to be a handicap in a way. I rather like the idea of going in to see somebody and having to write what he's got on his walls and exactly what he says.''

Much of the book concerns the uncertainty that Finch will ever put on a uniform, or that if he does, he'll not be able to stand the formal rigors or rituals of the American pastime.

The biggest problem Finch has with baseball, explains a character in the book, ``is that nirvana, which is the state all Buddhists wish to reach, means literally `the blowing out' - specifically the purifying of oneself of greed, hatred, and delusion. Baseball ... is symbolized by those very three aspects: greed (huge money contracts, stealing second base, charging for a seat behind an iron pillar, etc.), hatred (players despising management, pitchers hating hitters, the Cubs detesting the Mets, etc.), and delusion (the slider, the pitchout, the hidden-ball trick and so forth). So you can see why it is not easy for Finch to give himself up to a way of life so opposite to what he has been led to cherish.''

Plimpton says he feels the weakest points of the book are the imaginative parts, and the strongest are the sections based on factual reporting. The former include describing the other talents of Mr. Finch (he spouts Zen koans, mimics any sound, and pitches with one foot bare, and one in a hiking boot). The latter include knowledge of the administrative workings of the Mets, its personnel, training camp, and Shea Stadium. Early reviews say Plimpton couldn't write a bad novel if he had to, and that this one is a short, good read, maybe too short.

``After the article came out, I had discussions with [Commissioner of Major League Baseball] Peter Ueberroth, who said that if Finch continued to pitch perfect games he'd have to step in to do anything in the best interest of the game,'' says Plimpton. ``Then he said wryly, that he would force them to trade Finch to the last-place team, the Pittsburgh Pirates.''

Dr. Bobby Brown, president of the American League, told Plimpton he would suggest a new pitcher's mound ``for Buddhist overachievers - about 20 feet back from the regular mound that would give the batter time to bring the bat around.'' Plimpton says similar things have happened: In 1969, when pitchers were doing far better than hitters, the mound was dropped five inches and the strike zone made smaller.

As it stands now, the fastest pitchers ever clocked have been Goose Gossage and Nolan Ryan, at about 103 miles an hour. At that speed, the catcher can't even see the ball until it's about 20 or 30 feet from the plate.

Plimpton says Finch's pitches are ``just enough of a blur to know that it's not a magic trick.''

And it's the catcher that Plimpton feels sorry for. He writes: ``Every time that ball comes in, first you hear this smack sound of the ball driving into the pocket of the mitt, and then you hear this little gasp, this aiee! - the catcher, poor guy, his whole body shakin'.... It's the most piteous thing I've ever heard, short of a trapped rabbit.''