It is doubtful that 8,000 children have ever witnessed a single production of Puccini's gem of an opera, "Gianni Schicchi," before this week in this city. And perhaps some would think that a one-act comedy about death and greed should be off-limits for third-and seventh-graders.

But with television what it is, and so on, one need not have worried - at least based on yesterday afternoon's performance by the Children's Opera Theater.

It was one of those out-of-the-ordinary events that people pontificate about more than they do something to bring about a free exposure to love opera for impressionable young persons.

The theory is that opera wouldn't be so elitist if more of the young were exposed to it before it comes to sound too intimidating to venture toward. So the 2-year-old Opera Theater somehow got the money together, with the principal sum a $7,500 grant from the Downtown Jaycees, and put on a quite worthy version this week at the Warner Theatre.

Of course, not every youngster who gets to hear an opera is going to be carried away. That is not the idea.

There was a share of noncommittal "okays" from yesterday's seventh graders from Stuart Junior High in Northeast Washington. That was a euphenism for saying that opera didn't do much for them.

But there was also Otis Learch, a young man who had never seen an opera before, who observed excitedly, "Gee. It was just like "The Wizard of Oz." Larch said this is definitely not the last opera he plans to attend.

The Children's Opera Theater production is a creation of its full-time director, Micheal Kaye, and of various supporters - including, in particular, the Washington Performing Arts Society's manager, Douglas Wheeler. Wheeler's son Will also plays the little boy, Gherandino, and does it very appealingly.

Previously the Theater has been limited by meager resources - a budget of $30,000. It has kept lots of local singers busy, with concert performances, mainly at schools. It has given an estimated 500 such performances. But until this year, with a grant of $250,000 for salaries to artists from the Labor Department's Comprehensive Employment Training Act, full-scale productions were out of the question.

Yesterday's performance, one of five this week, was not the last word in Italian opera style. But it had its moments.

In the pit, the D.C. Youth Orchestra did itself proud. It was, for instance, better than many professional orchestras. The Schicchi, William Reed, was fine. And the La Ciesa was a particular delight, for personal as well as musical reasons. She was Ann Barzola, the former secretary and aide-de-camp to former National Symphony conductor Antal Dorati.