American Ballet Theatre favored us with a world premiere at the Kennedy Center last night. Antony Tudor's "The Tiller in the Field," set to music by Dvorak, like his previous "The Leaves Are Fading" (1975)9

It's a curious ballet, at once straight-forward and enigmatic, obvious and elusive-not at all untypical qualities for Tudor, but in some new combination that defies definition.

The audience received it warmly but without explosive enthusiasm, until the reticent Tudor himself was drawn onto the stage to share honors with Gelsey Kirkland, Patrick Bissell and the ensemble of 14 dancers.Tudor's appearance set off an ovation.

It was probably as much as tribute to Tudor's extraordinarily fecund and innovative career as to the ballet itself-a career which first burgeoned in his native England and then shifted to this country when Tudor joined the fledgling ABT in 1939. For the past five years, he's been associate director of the troupe.

"Tiller" shares with "Leaves" not only Dvorak's music (an overture and parts of two symphonies in "Tiller"), but also a wistful bucolic atmosphere and the general format of couples who sidle from strolling into dancing and back. But "Tiller" also has a plot, of fat boy meets girl, they fall in love and the love, shall we say, opens.

Ming Cho Lee's setting shows us the trees, meadows, hills and nestled cottages of a placid coastal village, delineated in flat, Chinese-lantern-style shapes and soft, fruity color-varieties of plum, mostly. Bissell, as a sort of rustic innocent, is lolling about, when Kirkland, as an oddly secretive lass, beings a flirtation beseeching him on bended knee to be her beau.

As the intervening dances, for the other couples become more amorous and animated, the romance develops, flaring into rapture by fits and starts, and eventually leabing Bissell the one who bows low. Then, at the end, comes a surprise of which there'd been a few fleeting premonitions-Kirkland doffs a jacket Bissell had thrown off earlier to reveal a tell-tale protruding belly, maybe the first pregnancy in ballet history.

It's hard to know what to make of this-what Tudor was after, exactly. As in his "Shadowplay," he hints more than he tells, but the resonances seem shallower here, at first sight. The movement is a s inventive and fluent as ever, though, permitting Kirkland to be at her most ravishing. Bissell, too, was excellent, as was the ensemble generally.