Rock musicians have performed regularly in prisons. So have theater groups. Now, classical musicians are joining the ranks. "Live Music Now," a nonprofit organization that recruits "emerging" young classical musicians to perform for the incarcerated and the institutionalized, has established a toehold in Washington.

Its founder and president is Yehudi Menuhin, who has started "Live Music Now" branches in Belgium, France, the Netherlands, Spain and Great Britain, where Menuhin founded the group in 1977. The organization sponsors close to 700 performances a year in Great Britain.

"Live Music Now," which here functions as an outreach program of the Dumbarton Concert Series, will send musicians to prisons, hospitals, psychiatric facilities and nursing homes.

"It's a way of reaching out to an audience that has no live music in their lives . . . or very little," says series Executive Director Constance Zimmer, who is planning a modest 20-performance season beginning this fall.

Leah Johnson, who codirects the "Live Music" program with Zimmer, is its American godmother. Johnson worked for "Live Music Now" in Brussels, and after returning to the United States decided to start a branch here. Menuhin has given the duo his blessing and is assembling a national advisory board for the U.S. branch. Meanwhile, Zimmer and Johnson are assembling a listening panel that will begin auditioning musicians in the next few months. Those who pass muster will be paid for their performances.

Most of the music to be performed will be chamber music, but Zimmer says that some folk and ethnic music will be included in the performance schedule.

The program means something else to the Dumbarton Concert Series.

"We've come full circle," says Zimmer. "This is our way of getting back to the kinds of artists we presented in our early years. We had gotten away from the emerging artists as the quality of the series improved . . . they are the ones who need to interact with an audience, who need an income."

Washington Ballet's Tour

The Washington Ballet will journey April 15 to Japan and Malaysia, where the company hopes to get as positive a response as it did last May on a tour of China.

The Japan leg of the journey is one that the ballet has waited a year to go on; Executive Director Elvi Moore said the group was invited back while still on tour there in January 1984. Because of scheduling difficulties, however, the company could not return to Japan last year. It is the Washington Ballet's first trip to Malaysia.

Overseas tours are an expensive proposition. A select group of Washington Ballet donors will be thanked for their magnanimity at a cocktail reception Tuesday at the residence of Japanese Ambassador Nobuo Matsunaga.

Northwest Orient Airlines is footing half of the ballet's $63,000 travel bill. Of that amount, $25,000 is for air freight. Along with the ballet's costumes, sets, backdrops rolled up in special canisters, lighting equipment for special effects, color gels, "hundreds of toe shoes," makeup and first aid (aspirin, cold packs, bandages and muscle relaxants, "for spasms") will go the floor, which weighs 800 pounds.

"We carry our own dance floor for the safety of the dancers," says Moore. The company is trying a different kind of floor on this trip. "We used to travel with a Marley . . . it's a vinyl type of a floor that makes the surface a much better surface on which to dance." The new traveling floor has a foam backing, which "adds a little bit of cushion," says Moore.

This time, the group will be paying for its own expenses while touring. When the Washington Ballet went to China, the Peoples Association for Friendship With Foreign Countries paid for all expenses within China; the ballet paid for transportation to and from China.

Associate Artistic Director Choo-San Goh, who has choreographed much of the group's program, is a native of Singapore, which is relatively close to the tour's last stop -- Pinang, Malaysia.

"He is very much appreciated in that part of the world . . . there aren't many choreographers from the Far East," says company spokeswoman Kitty Heflin.

Impressionism's Extended Hours If you don't want to head home after a day in downtown Washington, head instead for the National Gallery of Art: The gallery is extending the closing hours of its popular Impressionism show to 7 p.m. instead of 5 p.m. Monday through Saturday. Sunday hours, noon to 9 p.m., remain the same.