A century ago when it was new, the "Rigoletto" Fantasy for two flutes and piano by the brothers Franz and Karl Doppler must have wowed audiences. Focusing almost obsessively on "Caro Nome", it puts the music through variations Verdi never imagined and coloratura acrobatics beyond the reach of any soprano voice. While both flutists get a chance to show off the results of all those hours spent practicing scales amd arpeggios at top speed, the piano has several opportunities to play molto appassionato. This happens seldom when a piano's partner is a flute; the combination is so much like an elephant dancing with a butterfly.

Last night in the Tawes Theatre at the University of Maryland, this slight but charming piece (comically charming at this point in its history) was the only unfamiliar item in British flutist William Bennett's debut on the East Coast of the United States, and it was the one that came closest to perfection in performance--though the whole program was gratifyingly close. Bennett is a charmer when talking as well as playing, and he introduced this number with exactly the right touch of wit: "We present the original version of 'Rigoletto,' which was later scored for soloists, chorus and orchestra and played with great success in many opera houses of Europe." Clearly, we are dealing with not only a musician but a stand-up comedian.

When he was not delivering sparkling dialogue, Bennett delivered sparkling tone in a program that explored most of the flute's potentials except the avant-garde use of it as a percussion instrument: Bach's Sonata in B minor, Schubert's Introduction and Variations on his song "Trockne Blumen," and the flute version of Franck's Violin Sonata--once the exclusive property of Jean-Pierre Rampal, who was also playing it in the neighborhood last night. Rampal has recorded all of this repertoire except the Doppler brothers, which may be why that piece sounded best on this program.

But if Bennett on stage does not quite measure up to Rampal on records, Rampal in person also falls short of such carefully edited perfection. Bennett, who has been principal flutist with the London Symphony, the Royal Philharmonic, the English Chamber Orchestra and the Academy of St. Martin-in-the-Fields, displayed a star-class talent last night in a field that is becoming crowded with such talents. His breath control was superb throughout the evening and spectacular in the Franck, which is a challenge to a violinist and must be sheer torture to a flutist. He was particularly impressive for agility in fast passages, with phrasing that seemed as light and carefree as a spring breeze. His legato sometimes made a note seem to grow out of the one that preceded it--an effect particularly notable in the Bach slow movement.

His problems were those common to all flutists (though less so, perhaps, to Rampal): the instrument's limited emotional expressivenes and occasional unevenness of tone and dynamics--particularly a tendency for the top notes to sound louder and less rich than the others. But even mentioning these problems makes them seem more important than they were in performance. Pianist Clifford Benson showed considerable power used with commendable restraint, and flutist William Montgomery of the University of Maryland shared spectacularly in the fun of the Doppler piece.