The Washington Ballet is ending its current season in stunningly fine fettle, on the evidence of last night's concluding program in the troupe's Lisner Auditorium series (to be repeated this afternoon and evening).

The company looked stronger, more assured, more self-possessed - in a word, more genuinely professional-than ever, and furnished not only a number of noteworthy individual performances but also a sense of coherent, shared purpose throughout the evening.

Choreographically, the high court was the reappearance of "Synonyms," a ballet by resident choreographer Choo San Goh, set to the first three movements of Benjamin Britten's String Quartet No. 1 and featuring Robin Conrad and Julie Miles as dual principals, along with four pairs of men and women.

Like other of Goh's most trenchant works, "Synonyms" carries an immediate gut impact. Last night's performance-taut, incisive, intense-went right to the morrow of the choreography and its elusive, mysterious, oddly disturbing quality.

The two central figures, indissolubly wedded to each other even when far apart spatially, sustain an eerie tension between them that pervades the whole atmosphere of the ballet. They are set apart from the others not only by their dramatic black unitards and the spell they exert over the ensemble, but also by their movement-the imperious way they draw themselves up, the sharp flick of their limbs, the deep archings of their torsos.

Precisely who or what they represent is difficult to articulate-coexistent sides of a single self-absorbed personality, perhaps-but the unfolding of their presence rings true; we recognize its psychological accuracy and insight. And the plastic qualities of the ballet, its eccentric body contours, its bold floor positions and lifts, its pulls and preenings, give "Synonyms" a distinctive visual wallop.

Eric Hampton's "Tchaikovsky Sketches (Glances at a Smattering)," the evening's one new work, attempts a sort of good-natured battle of the sexes to four excerpts from Tchaikovsky's "The Seasons." At one moment, for example, a woman lifted high between two men literally boots her rival out of the way.

The humor is too sporadic, however, and sometimes out of keeping with the composer's Slavic romanticism.

Still there's no strained facetiousness, and Hampton shows a nice, casual ease in moving his eight dancers around the stage in legible patterns. A minor and disappointing effort, but nonetheless a confirmation of Hampton's promise.

Rounding things out was an excellant performance of James Clouser's theatrically striking, if choreographically thin, "Carmina Burana."