The portent of a new prodigy -- 17 year-old Gustavo Romero -- was in the air.

The celebrated Andre' Watts arrived early for Romero's concert at the Phillips Collection yesterday. Agents from New York had flown in to hear if what they'd heard about Romero was true. And there were distinguished Washington musicians, such as pianist Evelyn Hayes and her husband, impresario Patrick Hayes. The audience swelled beyond the usual Sunday afternoon Phillips crowd.

Before long the verdict was in. What they heard from the diminutive teen-ager, who looks even younger than he is, was a masterly recital.

It was not just a question of a youth with a brilliant set of fingers, which he has. And it was not just a question of a small person with enormous strength, though one cannot recall having heard quite such torrents of sound emanate from the piano at the Phillips.

Romero is already a sophisticated artist, though his potential may hardly yet have been tapped. Yesterday he showed superb agility (as in the glittering Scarlatti sonata that was the last encore), a command of sonority that a lot of major pianists cannot match (the range of color that he brought to Chopin's Sonata in B flat minor was both subtle and explosive). And he displayed wide stylistic diversity. There was the crisp, even, beautifully proportioned Haydn F major sonata, Hob. XVI:23. There was the alternating power and lyricism of the Chopin and the Rachmaninoff pieces. And there was the jarring, kinetic double fortissimo propulsion of the Prokofiev Seventh Sonata finale, which completed the written program--wonderfully articulated in places where it is often blurred.

Romero was not entirely unheralded. About a year and a half ago in San Diego he came to the attention of Zubin Mehta and Watts. He was brought to Juilliard on a scholarship in the "pre-college division." Mehta arranged for two concerts by Romero with him and the New York Philharmonic, one of which was later broadcast on CBS Television. That, of course, is precisely how Watts came first to public attention, with the Philharmonic on CBS under Leonard Bernstein. Watts said yesterday said that he has been keeping "close watch" on the pianist's progress. Romero is very much a pianist in the Watts mold.

As the concert unfolded there were few problems, either technical or interpretive. Criticisms are strictly a matter of degree. For instance, there will probably be a time when Romero can get a little more continuity of line out of the Chopin sonata's opening movement. The lyrical trio of the sonata's famed funeral march may someday be done more meltingly, though this might not have been Romero's fault--in the rapt treble melodic passages of both the Chopin and the Rachmaninoff the performance was impaired by a slight twanginess at that range in the Phillips' piano.

Romero is already a major talent. And it is based upon gifts that no teacher can give a pianist. The people at Juilliard and Watts and Mehta must simply help him to make the most of them.