Diana Ross has longevity-she is now approaching her 20th year in show business. Diana Ross has appeal-her beauty is complemented by seemingly boundless energy. Diana Ross has solid material-and this last may be the most important factor of all.

At Saturday night's Capital Centre concert, on sensed three distinct audiences, overlapping, but well defined. And Ross, the tactician, paced her show accordingly. After a spectacular entrance in which the star emerged from a projected image of herself, the show progressed through obvious plateaus: songs from the Supremes era; songs from Ross' two major films, "Lady Sings the Blues" and "The Wiz"; and a communally shared experience on Ashford and Simpson's "Reach Out and Touch (Somebody's Hand)."

In each segment, Ross worked her material elegantly, particularly the Billie Holiday songs. Though the oldest hits were abbreviated, Ross' effortless tussles with melody overcame the often overblown orchestra that occasionally appeared from behind the curtain.

Not surprisingly for a veteran, Ross worked hard. Except for two brief appearances by male dancers, she held the stage alone. When she wandered into the audience on "Reach Out and Touch," she displayed a gospel-like sincerity, provoking a genuine sense of camaraderie among the 10,000-plus in attendance.

For them, Diana Ross remains supreme.