"Absurdity," said Dr. Richard R. Baker, the Official Pronouncer, speaking clearly into the microphone. "A-B-S-U-R-D-I-T-Y," replied 12-year-old Richard Ary of Miami Beach, setting the theme of the 51st National Spelling Bee with the sixth word of the first round. The latest and largest of the annual two-day orthographic marathons was under way, plunging 106 contestants (eighth grade and under) into manic-depressive cycles of euphoria and . . . angst.

Billed as "a uniquely American insitution," the Spelling Bee meets that claim.Blame our language, whose spelling often has no relation to its sound. Such a contest would be meaningless in places like Italy or Russia where spelling is almost alphabet, the problems of running such a contest would drive a committee . . . berserk.

Clearly American, too, is the strong element of show-biz in the event. To find out who can spell best, the logical approach is a written test with everyone working on the same words; but then the audience would miss the spectacle of nervous schoolchildren halting, backtracking, asking for more information, breaking down and taking one small false step into . . . cataclysm.

"Deification," the final word with which 13-year-old Peg McCarthy of Holy Name School, Topeka, Kan., won a $1,000 prize, a large engraved trophy and a chance to shake hands with Rosalynn Carter today, was by no means the hardest word in the contest. Earlier, contestants had tackled "horripilation," "equinoctial," "antimacassar" "volitation," "ecdysis" and . . . deontology."

Equality of treatment is hardly possible in the traditional Spelling Bee format, where each contestant confronts his or her private word in solitary combat. In the first round, for example, one contestant had to spell "pizza" (and did), while another had to spell "oppugh" (and didn't). How a particular contestant gets matched to a particular word is an . . . enigma.

Failures come rapidly at the beginning; fewer rounds were needed to eliminate the first 60 candiates than the last six. Even at the superstar level (and all 106 participants were already champions, winnowed from 8 million starters), there are marked degrees of durability. At the very top, though, the differences are microscopic, the elements that make a contestant No. 1 rather than No. 4 largely . . fortuitous.

Girls, for some reason, seem to do better than boys; they were a substantial majority throughout this year's contest (as they are among the winners of previous Bees), and in the final rounds, after Scott Casper of Norfolk, Va., left the final "t" out of "guyout" (a flat-topped submarine mountain, as we all know), there were only four of them left, still pursuing . . grandeur.

"Hokku" was one boy's stumbling block (he used one "k", perhaps by analogy with the more modern form, "haiku"), and the incorrect "D-E-T-O-N-A-T-E-R" blew another's chances. The first to drop out failed, thematically, on "farcical" ("F-A-R-C-I-C-L-E"), but the early rounds, despite heavy mortality, seemed relatively easy: "dissaude" "foible," "nautilus," "ohm . . . hangar."

In a mere six rounds, on the first day, 84 of the 106 contestants were rendered . . . inoperative.

Just 22 survivors assembled the next morning for the final showdown, and the pace was perceptibly rougher: "atelier," "novena," "doclissimo," "obreptitious," "siccative," "epistrophe," each took its victim as efficiently as the sword of a . . . janizary.

Knowledge, literacy, memory; all play a role in forming a champion speller, but sitting there through two days, one cannot help wondering whether this test of raw skill and nerve in the pre-high-school set compared with other athletic events. Excellence is to be prized in all things, no doubt. But one wonders at the tumult and the shouting, the crushing disappointments, the fierce local pride taken in the results of a game not much superior to . . . Keno, lotto, monopoly.

Nostalgically oriented parents quaintly reminiscing - perhaps that is the reason for it all. In the struggles, the triumphs, even the bitter defeats, of these youngsters, we return vicariously, painlessly to the trials of the unknown, the exhilaration of getting away with a lucky guess - without, now, the former . . . neuroses, obsessions, preoccupations, and quiz regimens.

Should Topeka's unassuming victor wax xenophobic? Young zealots can be excused for seeing a curious pattern here: Topeka won the National Spelling Bee in '58, '68 and now in '78, and urban pride understandably seeks meaning in such patterns. But there will be other years and other Bees. There is still hope, Sedalia . . . Trenton . . . Unalaska . . . Villalba . . . Wabash . . . Xenia . . . Youngstown . . . Zanesville . . .