The Metropolitan Opera's "Lohengrin" kept getting better for nearly 4 1/2 hours last night at the Kennedy Center Opera House -- but it had begun with plenty of room for improvement. We may hope that the opening night's steady improvement is an omen for the New York company's week-long stay in Washington.

The Met will be here only half as long as it was last year, and on paper its casts and repertoire do not look nearly as spectacular. But 1984 was its centennial year and the Met sent out the best productions and singers it had. This year we are back to business as usual; the week began (despite some problems) at a decent, routine level of competence and there will be plenty of chance to improve in "Rigoletto," "Cosi fan tutte," "Simon Boccanegra," "La Bohe me" and "Eugene Onegin," not to mention Thursday night's repeat of "Lohengrin."

Meanwhile, if the company plans to bring back Wagner's drama of the mysterious knight who rescues, marries and then leaves a damsel in distress, three bits of advice might be pertinent:

1. Bring a swan.

2. Bring a tenor.

3. Bring a stage director.

Since "Lohengrin's" premiere nearly 140 years ago, the swan that pulls the hero's boat on stage in Act 1 and is changed back into a boy in Act 3 has been a colorful part of the opera, and for at least seven centuries before that the hero was known in legend as "The Knight of the Swan." It is invoked several times in the libretto ("Mein lieber Schwann") and mentioned in the Met's own plot summary for Act 3: "As Lohengrin prays, the swan disappears." Nothing to it when the swan is invisible to begin with.

It may be silly, but silliness is an essential part of opera. "Lohengrin" without a swan is like "Macbeth" without witches. And perhaps a hero who walks on at the beginning and off at the end is predestined to a pedestrian performance. At least, that is what happened to tenor Edward Sooter last night, singing the role that Placido Domingo had when the season opened.

His voice improved as the evening went along; the rawness of tone heard at the beginning gradually mellowed, but he never quite got rid of a wobble. He looks the part -- tall and (at least for this occasion) blond -- and he had a few galvanizing moments of stage action, notably when he killed Telramund in the last act, but his singing was seldom secure and even less often exciting. Teresa Kubiak was a decent Elsa but, again, unexciting.

In fact, the temptation was to cheer for the villains, Ortrud (Mignon Dunn) and Telramund (Donald McIntyre), who gave the best solo peformances of the evening. Villainous roles often give a singer more scope than those of the good guys, and in this opera the villains are more interesting if not more endearing than the knight who dares not speak his name. But Dunn and McIntyre -- most spectacularly Dunn -- took full advantage of every opportunity offered them by the text and music, while the stars seemed willing, most of the time, to settle into routine. This can be dangerous in "Lohengrin," which has many long, dry passages -- endless monologues with routine melodic lines -- that need an inspired performance to bring them to life.

The staging was splendid in Act 3, Scene 1, where the opera reaches its climaxes of sex and violence. It opens with the Wedding March (actually a postwedding processional to the bridal chamber) that is surely Wagner's most often-played music. Next comes a rapturous duet on the newlyweds' joy; Elsa begins to ask questions (understandably but with tragic consequences) about the identity of the man she has just married.

They are interrupted by Telramund and four co-conspirators, who break in with swords in hand and murder in mind, but Lohengrin kills the archvillain with a single thrust and the others immediately surrender. More happens in this half-hour than in the other four hours between the first and last curtains. And, given something to do, the performers do it generally well -- though nobody seems to know how the four supernumerary villains should act after the killing; they just stand looking helpless while Lohengrin finishes the scene.

The problems of stage direction come elsewhere, when the libretto does not offer anything simple and obvious to sustain visual interest. "Lohengrin" is essentially a Victorian melodrama wrapped in a medieval legend, and the Met production blends these elements by trying to look like a Pre-Raphaelite painting: quaint but static and slightly awkward in the positions the figures assume. The members of the chorus sing like angels, but too often they stand like statues.

Still, the chorus was, with the villains, one of the evening's glories. So was the orchestra -- given more substantial material than it has in many operatic scores and led with a sure and subtle hand by Jeffrey Tate. Giving his first performance in the Opera House, Tate solved from the opening bar a balance problem that many conductors never completely overcome there. Every vocal note came across clearly without sacrificing the richness of orchestral sound.