IN THE late '60s and early '70s, the Roberta Flack explosion was a Washington-made phenomenon.

The town was her musical launching pad and it claimed the former local schoolteacher and upstairs pub musician as its own, even though she was born in Black Mountain, N.C.

In her music she symbolized many trends of those evolving times, from the forthright message of black consciousness through the search for introspection.

Roberta Flack on stage: a hardy, yet feminine form, draped in flowing gowns, her billowing Afro following the bounces generated by the beat, head thrown way back, eyes closed and her mouth a valley of pleading, mournful, almost painful notes. Then Roberta would rise, because by that time everyone else was on the their feet, her tambourine hitting her side as she groaned, "Rev. Lee, do it to me."

She clicked, grabbing a few Grammys on the way, she once said, because "I've found out the way to get through to people is just to unzip myself and let everything hang out."

But, recently, Flack's only contact with Washington has been a few private parties and her fluid voice over the radio dial - "Strumming my face with his fingers," from her Grammy Award winner for 1973. Two years ago at her last Washington performance she was describes as "at her peak."

Though the silence is somewhat ominous Flack, who is 36, hasn't disappeared from the music scene. "Since it's been 13 months since the last album was released," she said in a phone conversation the other morning, "people think you aren't working. But I have been traveling, collecting new material and finishing a new album. You can't perform in Washington or New York without new staff."

Three years ago Flack sold her house in Alexandria, Va., to another musician, Gil Scott-Heron, and moved to New York City, commuting to [WORD ILLEGIBLE] Mass., where she worked on her [WORD ILLEGIBLE] the University of Massachusetts.

Two summers ago she married Steward Whitfield Bosley Jr., a film producer who has his own production company.

At the beginning of her ascent, Flack would say, "The songs have to have a message," and she worked hard to reveal successfully the inner dynamics and struggles of situation.

Has Flack, like many other voices of protest, been affected by the trend away from message to vacuous lyrics, often fattened with explicit sex lyrics? Will her new album, tentatively titled, "Blue Lights in the Basement," and scheduled fro July release, show a Flack tempered by the times?

"What we are experiencing now is the period where nonsense is fun. There was a period when nonsense wouldn't be accepted," she says. "Being creative is being able to provide both. People who don't make a contribution are those who don't change with the times.

"Yet there's a place for the message song today, but the time we are living in has another pulse Musically, it's livelier, even harsher Stevie Wonder's album represents a real change. It's a total absorption of everything you hear hear around you, not just one thought."

As of now the album has fewer balance than her previous ones and includes some [WORD ILLEGIBLE] and some MaRameyera blues numbers and five new songs by Eugene McDaniel a collaborator since the early days. "It's the best album I've ever done," said Flack, who is much thinner now and wears her hair in long braids that cascade onto her shoulders.

Her other projects revolve around the movies, both singing and acting. In December 1972 it was announced that Flack would play blues great Bessie Smith in a film biography but those plans have been scrapped because of fund-raising difficulties. The group Flack was working with retains all the rights to Chris Albertson's Smith biography and the Smith family sanction, but since Berry Gordy, the head of Mutown Industries, has decided to do a movie of Linda Hopkins' nightclub and theater treatment of Smith, Flack isn't interested anymore.

On her schedule, besides acting lessons, were two soundtracks, one who Curtis Mayfield for Sidney Poitier and Bill Cosby's second sequel to "Uptown Saturday Night," and Richard Pryor's new movie "Greased Lightning."

During a recent overseas appearance, an East European journalist asked her it she was a happy woman.

It took her by surprise, "I told him it was an odd question because the audience had been excited, I had been bubbling, bouncing around, grinning, obviously radiating from my Fashion Fair cosmetics," she says. "But I'm very happy. Happier than ever, I would probably only be happier if I could push a button at a moment notice and be anywhere I wanted."