Probably the most spectacular moment in Gian Carlo Menotti's newest opera comes when a Plutonian spaceship lands in a typical American backyard, with a cascade of electronic notes, a roar of jet engines and a lot of flashing lights. Inside the house (whose walls have suddenly become transparent), the family runs to hide under the kitchen table, and "A Bride From Pluto" becomes a Close Encounter of yet another kind.

The real encounter, of course, is that of opera and fans--of "A Bride From Pluto" with the children who are its primary audience. A few children were in the Terrace Theater last night for the world premiere, but not a critical mass--not enough to gauge the reaction when it is performed for an audience entirely of children, able to react freely without the daunting presence of adults. I suspect that such audiences will react very enthusiastically, once this work becomes (as it will, like "Amahl and the Night Visitors") a traditional part of their lives. And if they tend to like it for reasons only dimly related to its stature as a work of art . . . well, that has happened often enough in the world of adult opera.

The first thing to be said about "Pluto" is that it is show biz and totally professional from beginning to end. On one level, it is a simple, fast-moving story with a plot and characters that anyone in grade school can understand and enjoy. It is spectacular, particularly in the spaceship episode and the well-choreographed antics of the soldiers and ladies-in-waiting who accompany the Queen of Pluto on her husband-hunting expedition to Earth. And it has a neat, humanistic moral that ties in nicely with the final twist of the plot. Not unimportant for its potential at the box office, it has a little robot, obviously a distant cousin of R2D2, who sings not a note but fills a strong supporting role. These seem to be the ingredients of a hit.

Musically, the opera is pure Menotti, which means it is about as melodious as anything being written for the opera stage these days, and perhaps a bit more sophisticated than an opera for children really needs to be. The primarily adult audience on opening night obviously enjoyed it, not only for some of the things that will attract children but for its sly digs at subjects that ranged from rebellious youth to science fiction to the coloratura soprano voice.

It would be hard to imagine a more lovingly crafted production than this one. All five singing roles are strongly cast, particularly Pamela Hinchman in the role of the Queen of Pluto and Nicholas Karousatos as Billy, the typical, spoiled-rotten American boy who nearly becomes her husband. Dana Krueger is outstanding in the relatively small role of the mother, and Robert Keefe and Camille Rosso perform commendably as Billy's Father and his girlfriend, Rosie, who makes the plot come out right in the end.