It was the night Bella Hatfield and Vance Marshall had waited 25 years for.

The two friends had practiced Mozart's Concerto in E Flat Major for Two Pianos for more than a year. Saturday night, in front of 1,350 people, they were about to make their duo debut with a symphony orchestra in Fairfax High School's packed auditorium.

Dressed identically in mauve chiffon evening gowns, pearl earrings and silver high-heeled shoes, the women paced nervously backstage among empty violin cases, chairs, sheet music and costume racks loaded with overcoats. On stage, the Fairfax Symphony played its opening selection, "Prelude to Amelia Goes to the Ball" by Menotti.

Hatfield fidgeted with her hair and checked her makeup. She slowly leafed through the blue music book as if to study the notes one last time before the performance.

Marshall methodically wiped each finger and the palms of her hands with a lace handkerchief. She whispered to a visitor that she remembered to bring a Hershey bar to eat after the concert, a ritual Marshall has practiced since she was a child.

"Why, Vance, I've never seen you with so much makeup on," Hatfield said, as she looked approvingly at her partner. "You look lovely."

Marshall smiled and squeezed the handkerchief. As the symphony finished the sprightly Menotti piece, Hatfield rubbed her hands together and wiped them on her dress.

Symphony conductor William Hudson came backstage to escort the women to the two nine-foot grand pianos set up in front of the orchestra.

"Are you ready?" he asked.

Hatfield and Marshall looked at each other and nodded. They had been ready for 25 years.

Between the two of them, Hatfield and Marshall have been playing the piano 120 years. Marshall, who was famed pianist Rudolf Serkin's first American piano student, said music has been "the major interest in my life . . . . I would have been a professional had I not married and had a family."

Hatfield, Marshall's friend and partner for 25 years, has taught piano full time to adults and children for more than a half-century. This past summer, when their practice sessions intensified, Hatfield's life was consumed with rehearsals, piano lessons and still more rehearsals late into the night.

The women frequently perform together for various social and cultural organizations in the area. They are regulars at the Friday Morning Music Club, a group of professional and amateur musicians that holds weekly concerts for its members, and play at fund-raisers for professional music organizations, such as the Northern Virginia Music Teachers Association and the Virginia Federation of the American Federation of Music Clubs.

"We feel the music the same way," said Marshall, when asked the secret to being a successful piano duo. "She Hatfield has a much larger hand than I do so I have to use somewhat different fingering. But how she accomplishes it or how I accomplish it isn't really important. How it comes out is what counts."

Marshall, 69, has played the piano since she was 7 years old. She taught herself to play "by ear" without the aid of an instructor and still uses the same Baldwin grand piano she practiced on as a child.

Almost all of her friends are musicians, said the Webster Groves, Mo., native, and they often have impromptu concerts at her house in Oakton. "There's something very social about doing that sort of thing with other people. If you really go at it for five or six hours by yourself, it can get very lonely," Marshall said.

Hatfield, 71, studied piano at the New England Conservatory of Music in Boston and later at the prestigious Juilliard School in New York. She still plays on the same black Steinway she practiced on as a teen-ager in Schenectady, N.Y.

Hudson, who in addition to being conductor is music director of the 106-musician symphony, said he asked Hatfield and Marshall to perform because "they are two of the best soloists in the Virginia area . . . . they can really communicate the spirit of the music to an audience in an effective way."

When the concerto ended, the audience stood instantly and erupted into a five-minute thunderous applause. Hatfield and Marshall, looking a bit dazed and breathless, bowed gracefully and accepted bouquets of flowers from their children, who had flown into town for the occasion.

Three bows later, the women walked backstage to a waiting throng of friends, admirers and family members all wanting a hug or just to tell the pianists how much they enjoyed the concert.

Marshall, looking a bit weary and shaken by the excitement, said this was her last performance in the area for a while because she and her husband were moving to Ohio.

But that was irrelevant right now. There was a private reception in their honor after the show and then a chance to spend time with their children.

Above the noise and exuberance that filled the crowded room, Hatfield and Marshall glanced at each other and grinned. It had been worth the wait.