L'Orchestre de la Suisse Romande, which played yesterday at the Kennedy Center, has long been familiar on records under the baton of its founder, Ernest Ansermet, whose rather dry sound and analytic approach conveyed both enlightenment and enjoyment.

Ansermet retired 17 years ago, and his orchestra now sounds more opulent in tone, virtuosic in its technique and precise in ensemble playing. Music director Armin Jordan is hardly responsible for these improvements; he has only held this position since September. But yesterday on the Concert Hall podium, he took full advantage of the work of his predecessors in Geneva.

All the music was modern, and most was French: the short ballet "La Pe'ri" of Paul Dukas and the familiar "Pre'lude a l'apre s-midi d'un faune" of Debussy and "La Valse" of Ravel. Jordan phrased flexibly, balanced the sound delicately and found an effective middle ground between clarity and suggestiveness.

The only non-French items on the program were associated with guest oboist, composer and conductor Heinz Holliger, who soloed superbly in the oboe concerto of Richard Strauss (a little masterpiece of his final years) and conducted his own "Tonscherben," a well-crafted series of "orchestral fragments."

On the evidence of this concert, L'Orchestre de la Suisse Romande may be one of the two or three best French orchestras in the world. DeReggi Interart Ensemble

Gaius Valerius Catullus died about 2,040 years ago and still lives today, as the DeReggi Interart Ensemble demonstrated last night at La Maison Franc,aise, the superbly designed and equipped little theater in the new French Embassy.

Catullus was the first modern poet -- the first who broke away from formalism, sang of romantic love and chronicled his own identity crisis. Appropriately, he was given modern treatment, with slide projections, electronic sounds, miming and dancing, an atonal chamber ensemble and instruments of eerie beauty (the "tree harp" and "rain saucer"), made from found objects.

Three poems set by Lawrence Moss were witty and poignant, with spare-textured music that enhanced the words. Ric Wagner, aided by striking mimed and projected visuals as well as his invented instruments, wreathed the old texts in fresh, brilliant invention. Vincent McDermott blended two poems in a psychodrama for soprano, viola and dancer, while John Van Buren used the Latin texts in a cycle for soprano and chamber ensemble. The protean genius of the witty, obscene, flippant, brooding poet was well-served throughout the evening, under the general direction and with the frequent participation of soprano Marilyn Boyd DeReggi.

The same group will present a program of John Cage's vocal music next month with Cage participating. It looks like interesting times ahead in this exciting new performing space.