FORREST GUMP by Winston Groom (Doubleday: $14.95; 202 pp.)

Forrest Gump, the narrator and more or less hero of this intermittently affecting novel by Winston Groom, is a 6 feet 6 inch 240-pound good ol’ feller from Mobile, Ala., with an IQ of 61. “Let me say this,” Forrest says right off, “bein a idiot is no box of chocolates.” On the other hand: “At least I ain’t led no hum-drum life.”

Not hardly. Hauled off the street at 16 to play high school football in the 1960s, the hulking Forrest sprints his way to a slot on the university team, bunking in “the Ape Dorm” with the rest of the players coached by Alabama’s Bear Bryant. Forrest and company steamroll past the opposition and make it into the Orange Bowl before disaster strikes--a typical finale to Forrest’s escapades.

More adventures follow. Forrest is drafted and lands in Vietnam in time for the Tet Offensive. “Things is very primitive in the jungle,” he notes, and the chaos of the war confounds him. “It is somthin I simply cannot understand--why in hell is we doin all this, anyway? Playin football is one thing. But this. . . .” Despite his puzzlement, he’s good in combat, wins the Medal of Honor and gets to watch “The Beverly Hillbillies” in the White House with L.B.J.

Then Forrest becomes a Ping-Pong ace and travels to China, where he saves Chairman Mao from drowning. Forrest, part of a top-secret NASA project, is sent into outer space with a grumpy female major and a male orangutan named Sue. Forrest makes (and blows) a bundle as a pro wrestler called “The Dunce.” Forrest plays “The Creature From the Black Lagoon” in a movie starring Raquel Welch. All the while, he carries a torch for his first-grade sweetheart, Jenny, whose affection he wins and loses time and again.

The notion of a fictional “idiot” enduring various real-life regional and national idiocies with folkwise equanimity is not without charm; and in the early chapters of this hayseed’s progress, Forrest earns his fair share of sympathy. Part Candide, part Huck Finn and a whole lot of Andy Griffith, he makes his case in a voice all his own; and the generous reader will not be unmoved by certain wispy sentences that tug at the heart like hound dog pups that are starved for love.

Trouble is, by the time Gump blasts off in that space ship, we’ve departed his endearingly oddball reality for a Cloud Cuckoo-land where slapstick is king and bodily functions are the root of all humor. Once our boy is taken prisoner by cannibals (with a Harvard-educated chief, no less) the respect Forrest worked so hard to earn in the first pages is about used up. At its ugliest, “Forrest Gump” degenerates into a sexist, racist cartoon of numbing dumbness.

Seems a pity to have gone to the trouble of bringing poor Forrest into the world just to sell him out for the cheap shot, the cornpone snigger. Even Forrest knows that “folks sposed to be kind to the afflicted.”