It takes more than an ordinary infusion of inspiration to bring American Ballet Theatre's aging production of "Swan Lake" to life these days, and last night's performance at the Kennedy Center, opening the company's three-week run in the Opera House, didn't make it.

Technically speaking, ballerina Cynthia Gregory in the dual roel of odette-odile and her partner Fernando Bujones as Prince Siegfried, like the sterling virtuosos both of them are, danced extremely well. But if either of them had their hearts in it, it didn't show.

"Swan Lake" is, to begin with, a dramatic ballet-a fairy tale about a young man who discovers true love, yeilds temporarily to the blandishments of false glamor, and is redeemed by ultimate sacrifice. But last night's performance had no drama-no tension, no suspense, no credible passions.

When it is transfigured, as it can be and sometimes is, by dancing of profound sensibility, then "Swan Lake" becomes more than a pretty, romantic thle and assumes the dimension of myth.

Gregory, as she's shown us in the past, is certainly capable of this level. But dance is a volatile art, and dancers have vicissitudes of spirit. Last night seemed a downer for her.

Was it the musical performance, which was led by ohn Lanchberry in the perfunctory manner of a conductor who's been through the Tchaikovsky score once too often lately? Was it the lack of emotional connection with Bujones, whose acting looked bland and conventional last night?

The production itself, which is 12 years old, must be counted as a depressive factor. The costumes look slack and dingy, and the sets, despite the continuing magic of Oliver Smith's conceptions for the lakeside scenes, are going stale, too.

But the real problems are not physical. As originally staged by England's since-deceased David Blair, the production sustained years of vitality and dramatic excitement. But it now looks as if no one's minding the store.

Dancers get on stage somehow, go through the required motions, and exit and that's about it-there's no action, and there's no interaction. The men and women who populate the stage in nondescript poses and gestures are no more like real courtiers or huntsmen than Park Avenue door men are like real generals.

The corps de ballet danced very creditably in the "white" Acts Ii and Iv, and Janet Shibata and Cynthia Harvey gave us a more than presentable pas de trois in the first act with Bujones as their partner-an unusual participant in that most Siegfrieds in the ABT version watch from the sidelines as another male dances.

But the third act divertissements were mostly a shambles, illegible in pattern, slovenly in rhythm and ensemble, stylistically ragged. Gregory and Bujones turned on the electricity for the Black Swan sequence, all right, but her sharp glitter as Odile and hss bursts of bravura were just isolated stints of shownship in an emotionally inert ballet.

Perhaps one should take heart, though, as far as the rest of the run is concerned-ABT's last winter season began as a drag too, and proceeded nevertheless into much magnificience.