Two men pressed their noses against the display window of the Soul Shack, mouthing the words of The Jones Girls' hit song as its catchy verse hung in the humid air of G Street."If you ain't loving me, who in the world you love, tell me if you don't want me around."

Inside, the three sisters softly mouthed the words, and a few fans couldn't resist dancing to the crisp, floating beat of the song that has taken the singers from praised anonymity as background vocalists for Diana Ross to the season's hot contenders for the mantle of best girl group. "You have a lovely future," whispered Dukie Brown, 36, an employe of the Government Printing Office.

The sisters smiled as one, the dazzling cover-girl smile used before pouts were discovered, and they continued signing glossy photos and artsy album covers in bold blue, purple and black signatures. "This is the chance to get near people, let them know a little about us," says Shirley Jones, 25, the oldest.

"And you know what's happening?" she adds, thumping a four-inch scarlet nail into her hand. "People are beginning to say The Jones Girls, instead of those girls who sang behind Diana Ross."

A clear-cut identity, that's one of the aims of the promotion tour. It's worth the broken-down limousines, long stints behind record counters, and rushed visits to disc jockey cubicles, the tissue box spaces that offer a link to thousands of ears and pocketbooks.

The golden age of black girl groups was 15 to 20 years ago when the Shirelles, the Chantels, the Supremes and the Marvelettes dominated the airwaves and inspired first romances. But successors with staying power have been scarce. The Three Degrees, the Emotions, Sister Sledge, Taste of Honey, a recycled, silver-plated version of the old Patti Labelle and the Bluebells, and updated versions of the Ross-less Supremes have tried, but each seemed to lack one or another of the key elements. Ideally, a lasting girl group should have strong, interchangeable voices, cool, grabby lyrics and enviable good looks.

As for The Jones Girls' chances, Shirley Jones feel the recent success of women singers has to help. "We can't say what's going to happen to us but it is the time for women," she says, holding back a smile.

During one break in their three-day blitz of Washington, The Jones Girls put on bedroom slippers in their hotel room, planned a long, leisurely dinner, and talked about their careers.

Like many black groups, the sisters received their musical initiation in gospel, singing with their mother. But they were especially blessed; their mother, Mary Frazier Jones, is one of Detroit's best gospel singers.

"In our teen years we spent a lot of time trying to get a hit record. People were always saying we were too young, couldn't have the success too early," says Shirley Jones. In 1969 they signed with Joy Roll, a local Detroit label, and in the next six years had almost a half-dozen contracts.

Valorie, 23, adds, "All the experience helped us to be strong. We worked hard, we sent post cards to the stations because we heard that helped."

However, even in the depressed music circles of Detroit after Motown Records moved to California, competition remained stiff. The sisters had a local hit in Chicago, but then Shirley Jones moved to Los Angeles. She enjoyed a busy period of background singing, working with Cher and Freda Payne, and doing the theme for the television series, "That's My Mama."

But projects for all three sisters were scarce. In Detroit, Brenda, 24, and Valorie continued to do background $&(WORD ILLEGIBLE sessions, Brenda also taking some psychiatry courses at Wayne State University, Valorie studying keypunch.

Then one week when all three were together in Los Angeles, Diana Ross held tryouts for a background group. With the exception of their mother, Ross had been their only idol.

"When we were 7, 8 and 9 years old, we were into the "Supremes at the Copa" album," says Brenda. "My mother made us top hats and canes and we imitated the group to death."

"We were very nervous about the audition because she was there," recalls Shirley. "Brenda almost fainted."

Yet, within a week, without Ross knowing the trio was also from Detroit or had been fans who had helped push her to the top, The Jones Girls became the nameless faces behind her road act.

Tours of Europe, the United States and Japan followed. And Ross remained their idol.

"When she had time we would talk," says Shirley Jones.

"She told us how she would watch other acts on the Motown Revue, like the Contours," adds Brenda Jones. "She would take a little bit of this and that and come up with her own thing.

"She also said she wanted to help us."

One night in Philadelphia The Jones Girls were teetering high on scaffolding behind Ross, providing the smooth dowahs and oohs for the star. In the midst of her routine, Ross shouted, "Hey Kenny Gamble, look at the talent I've got up here." With that impetuous shout to the most successful rhythm and blues producer of the last 10 years, Ross removed the cloak of namelessness that buries background singers, and paved the way for their break.

A year after that impromptu audition for Gamble, The Jones Girls were signed to a four-year contract for Philadelphia International. Their first single, "You Gonna Make Me Love Somebody Else," is No. 5 on Billboard's produced by the best of Gamble's talent, rests for the second week at No. 9 on Billboard's R&B album charts.

"Our sound has a quick identity. It's easy listening, with a spirit, and we're light, owing a lot to gospel and disco but without their loudness," says Shirley. Though their themes are about love, the trio doesn't plan to follow the explicit trend of women vocalists.

"People are opening their minds, allowing more freedom in lyrics," says Valorie Jones. "We think we can keep the truth about love relationships going without singing about joining me in bed."

At the Soul Shack, a fan spoke of the girls' harmony and clarity, saying, "They can take over where the Supremes left off." At those words, Valorie Jones, almost hidden underneath a picture-window black straw hat, started to sing.

No longer bound to imitating or filling in someone else's pauses, she has her own song now, with a warning: "If you don't treat me the way you do..." CAPTION: Picture, The Jones Girls, from left: Shirley, Brenda and Valorie; by Fred Sweets - The Washington Post