THE WORKS of Carlisle Floyd, the opera composer-librettist, do not have quite the crowd appeal of those of Pink Floyd, the rock group, but that doesn't mean he's not working on it.

Just a few weeks ago, for instance, his "Of Mice and Men," opening a three-week run at the Kennedy Center Tuesday, was given a series of free performances in the parks of Houston.

"I've never been in an audience like that," marveled Floyd, a courtly fellow seemingly not given to emotional excesses. "There were stevedore types, children hanging over the orchestra pit, people drinking beer wandering in and out.I don't know where they came from, but they seemed intrigued, absorbed."

All of which is just fine by Floyd, who feels "opera should be an enormous popular medium, it always was, and that doesn't mean pandering or prostituting one's art or whatever." Floyd even shies away from the word "opera," prefering to call his works musical dramas, "theatrically viable, musically rewarding," so as to stress the equality, the balance of the two components.

"Opera in this country has always been something of a hothouse flower; certainly not the girl next door, it carries some kind of a stigma," Floyd explains in a let's-face-facts tone. "There is a very large American audience of rather well-to-do upper-middle-class people who are very disaffected from opera. They like the symphony, art, film, but they're simply turned off to opera."

This lack of interest is rooted, Floyd feels, in the traditional realism of American popular culture, a realism that holds no truck with the plots of most operas. "Librettos often strain credulity, to say the least," Floyd says. "Some of those plots ought to be kept confidential."

Making all this even worse is the insistence of purists that operas always be given in their original language. "I'm doing everything in English," says Floyd stoutly. "You'll never find a composer who doesn't want his work understood. Even Strauss was appalled when he came over for the American premiere of 'Der Rosenkavalier' to find it was being done in German.

"You'd be annoyed beyond belief if you had to sit through a foreign film without dubbing or subtitles, yet people are glibly expected to sit still for three hours with only a vague idea of what's going on. It seems so needless to me.

In pushing to make opera "a more immediate kind of experience," Floyd must not only contend with the traditionalists, people who "aren't interested in anything but who the new singer in the new production is," but also with dissatisfaction from the other camp, the musical comedy audience that wants "nothing that smacks of anything serious."

"We have musical comedy, why shouldn't we have musical drama?" Floyd asks, not without reason. "Ninety per cent of Broadway composers, and I don't think of this as a putdown, are tunesmiths. They have great gifts for coming up with melodic lines, but they don't have the training to turn out an overall, compositional fabric. And something that requires emotional range is way outside the limits of where musicals can go."

Which is just about where "Of Mice and Men" comes in. Next to "Susannah" it's the most successful opera he's done, and Floyd says he was attracted to it initially because it was "a curious story. You take away from it a feeling of great tenderness, but it abounds in the kinds of violent situations that are the staff of opera. In the last act alone, there are two murders and a fight on stage."

Though the idea of putting "Of Mice and Men" into operatic form seems to give everyone a start when they first hear it, audience reaction has been keen. Floyd credits "an old Boston dowager," with his favorite words of praise, though "she didn't mean it as a compliment. 'I've been going to the opera for 50 years,' she said, 'And I never wept before.'"

To Carlisle Floyd, that's progress.