PUPPETS AFTER DARK - At the Golden Booeymonger, Connecticut Avenue and R Street NW, through May 20 at 8 p.m. Tickets are $5 and light suppers are available. Call 927-5599 for reservations. Because of the length of the program and the sophisticated nature of the material, "Puppets After Dark" is not recommended for children under 10.

Jo Ann Stephano Young, featured singer for the Blue Sky Puppet Theater, was belting out an aria during a recent elementary school performance when she noticed a stirring in the audience. A young fan commenting on her ability?

No, just a little girl throwing up.

"It had to have been my singing," Young laughed later. "What else could I think? They hadn't had their lunch yet."

That kind of audience reaction is not the reason the Blue Sky puppeteers are playing fewer elementary schools these days, but it's an occupational hazard they presumably won't run into during the next week and a half. "Puppets After Dark," their trilogy of experimental plays at the Golden Booeymonger restaurant, is designed to appeal to an adult audience.

"There was no market for this when we first started out five years ago," said Bule Sky's founder Michael Cotter, dressed in rainbow suspenders and a sky-blue T-shirt, "There were always lots of children's groups, but nothing for adults - at least, not in Washington." Now the Muppets are winning the television ratings game and, although puppet dinner theater may not be the first thing that comes to mind when planning an evening out, the popularity of puppetry is definitely on the upswing.

It's an act form, they feel, that should be taken seriously as well as appreciated for its humor. The three shows in "Puppets After Dark" highlight the medium's versatility: "The Barker of Seville," a slapstick comic opera heavy on the puns, is followed by "Hands Off," an abstract psychological piece written to accompany a cello quartet.That, in turn, is followed by broad political satire in "The Puppet President."

"Puppet President" is funny and "Hands Off" an interesting experiment, but the group's talents are shown to best advantage in "Barker," a cleverly written, engagingly acted show starring a dog, a fish, a girl and a large banana. Written as a showcase for Young's striking voice, it combines opera and rock music with humor both gentle and outrageous to affirm Blue Sky's basically optimistic outlook on life. Young's duet with the villain Leonardo Fullabaloney is a comic highlight, and the denouement, a grocery store scene in which a dog sings the well-known operatic classic, "Fig Rolls," is hilarious - it would be a great way to introduce a child to opera. Or an adult, for that matter.

Cotter, 31, a former schoolteacher, carpenter and Peace Corps volunteer, discovered puppets by accident during a trip to San Francisco. "I was 26 and it was the first time I'd seen a puppet show. It was a very joyous experfence. I found myself grinning from ear to ear watching the thing. It was wonderfull I'd never seen anything like it back in Washington." He came home to found Blue Sky.

He and the other members of the troupe - Young and her husband Jeremy Young, both 31, and Joe Pipik, 27 - spent the next few years refining their act performing everywhere from Elk Clubs to the Ellipse. During the 1976 presidential campaign they did political satire on the street. "It was the same concept as an ice cream truck. We had a van and a vendors' permit, and we'd put out our little blue box with the clouds in it. It was a real strain, cops knocking on the windows, arguing with drunks, but a very exciting time, and a fascinating proving ground for the company. The audiences were fantastic. If the material wasn't real hot they'd just walk away."

"Street theater" has a hippieish ring to it, but the Blue Sky puppeteers are not starryeyed flower children. They're looking for a business manager, talk in terms of royalties and spin-offs, and are interested in exploring the areas of educational records for children and radio theater ("I love radio, I can't take my ears off it," says Cotter).

They are serious artists, not just comedians. Jeremy Young is a conductor and accompanist and has a master's degree in composing. Cotter, the company's director and producer, is also a flautist. Pipik is a guitarist, mandolinist, siner, juggler and writer. Jo Ann Stephano Young teaches piano and is alto soloist at Annunciation. Church on Massachusetts Avenue NW. "'Barker' is an incredible vehicle for me," she says. "It's a chance to sing opera."

Puppertry seems the logical way to combine all these interests. "All the elements of theater are there, in a contained space," Cotter begins, explaining the appeal.