The return of ''The Wiz'' could qualify as an exuberant gesture to family fare and summertime fun. The 1975 surprise hit musical brings back Stephanie Mills, the Dorothy of the original production. The still youthful-looking Miss Mills is surrounded by a new cast of principals to play the fantastic creatures drawn from the L. Frank Baum childhood classic, ''The Wonderful Wizard of Oz.''
Now as then, the show's prime assets begin with the largely upbeat score by Charlie Smalls. Musical moods range from rock to soul and from jazz to gospel. Geoffrey Holder again serves the extravaganza as director and wizard of costumes. Charles H. Coleman handles the musical direction. The opening night performance at the Lunt-Fontanne was repeatedly interrupted by welcoming applause and even an occasional ovation.
Perhaps this momentum will once more carry the day for ''The Wiz.'' Unfortunately, the show seems to have gotten considerably out of hand during its months on the road. While Miss Mills continues to give a winning and strong-voiced (or strongly amplified) performance, too many of her fellow players are self-indulgently hamming it up. In line with a well-known George S. Kaufman anecdote, Mr. Holder might well have called a rehearsal ''to take out the improvements.''
Notwithstanding the energetic dash and dazzle of the George Faison dances and designer Peter Wolf's succession of scenic effects, ''The Wiz'' lumbers ponderously through its familiar paces. ''Ease on Down '' remains the highlight of Mr. Smalls's agreeable score. But the inspirational message of ''If You Believe'' appears to have become diminished. In any case, a raucous amplification system renders many a lyric incomprehensible. ''The Wiz'' still rates as family entertainment for those who can afford Broadway prices. But it's not the fabulously high-flying extravaganza it used to be.