Handel the opera composer is alive and well, judging by the enthusiastic reception given the American premiere of "Radamisto" Saturday night. Reacting like a London audience of 260 years ago, the Kennedy Center audience forgot the dramatic absurdities and succumbed to the music, brought vividly to life in a spirited performance under Stephen Simon.

He has put together a performance version of exceptional coherence and variety. Each scene made dramatic sense by itself, and transitions between scenes worked well. Except for an awkward shift from Zenobia's aria into a rapid orchestral passage at the end of Scene 4 in Part II, the music flowed easily with frequent changes in pace to hold one's interest. The opera was in danger of sagging in the middle of the second part, but at that point Simon inserted the evening's first duet, and its freshness restored momentum.

If glorious music was ommitted, it was not missed. From the powerful "Simon Dei," with which the opera opens to the exuberant closing chorus, Handel's vital and fertile imagination seldom falters and frequently surprises. Radamisto's "Doice bene di quest'alma" sounds amazingly like Mozart. There are many lovely orchestral solos, and without question the most dazzling music in the entire opera is Polissena's aria, "Sposo ingrato," with it virtuoso exchanges between voice and solo violin.

Benita Valente's clear and brilliant interpretation turned this aria into a show-stepper, capping for her an evening of higly expressive and vocally pure singing. Beverly Wolff made a strong Radamisto despite tendencies to inject a 19th-century heaviness of style into her performance and to force the upper tones.

Hilda Harris' portrayal of Zenobia possessed vocal richness and nobility of manner. Bass Kenneth Bell was a suitably proud Farasmane and tenor Richard Lewis, though his voice lacked resonance and agility, brought considerable style to the role of Tiridate. Nancy Shade made an enthusiastic if occasionally uncontrolled Tigrane and Linda Mabb's soprano aria was notable for its light, graceful ornamentation.

Spurred on by Simon, the orchestra, in particular the continuo, played with a freshness and precision that animated the entire evening.