She went out there a youngster Saturday night, and she came back a youngster. Mary Moltrup -- who sang "The Star-Spangled Banner" at President Reagan's inaugural gala and stole the nationally televised show -- is, after all, just 7 years old.

"It was fine," the Beltsville girl said yesterday in the afterglow of her stellar performance for the Reagans at the Washington Convention Center. "I felt very funny and excited. The people were everywhere. I was thinking -- I don't know what I was thinking. About the words, I guess."

When it was over, said her voice coach Linda Townsend, Mary asked, "Can we go up to the dressing room and sit down and do some coloring with my crayons so I can relax?"

Then Mary collected Tom Selleck's autograph.

"Can you imagine the kind of performance she had to give to sing that song?" said gala talent executive Danette Herman. "That's a hard song to sing, but she came through like a trouper. We were all in the green room holding our breath for the high note on 'free.' When she got it, we all started cheering."

"I don't know if I should say this," said Townsend, "but she was wearing white tights with her royal blue dress, and the tights wouldn't stay up because her legs are so tiny. So we had to hold them up with Little Boy Blue suspenders."

Mary, a second-grader at Calverton Elementary School who performs regularly as part of the singing Moltrup Sisters, was chosen to sing the national anthem from a score of children -- including her 10-year-old sisters, twins Diana and Wendy -- after an audition Jan 4.

Four feet tall, with blond tresses and blue eyes, she had no trouble getting the gala producers' attention. "She was such a sweet little girl and very poised," said Herman.

"I think we're a little bit in shock and we're very pleased," said Mary's mother, Janie Moltrup. Her father is Lt. David Moltrup of the Bethesda Fire Department. "We're trying to get used to the idea that our darling baby girl has been able to sing for the president of the United States and represent the children of our country."

At the curtain call Saturday, Mary took the stage with her fellow performers and said hello to the Reagans.

"I gave the president some jelly beans and I gave his wife some gummy bears," she said. "They're little things that are bears but they're icky and sticky. The Reagans said, 'Thank you,' and then the president bent down and kissed me.

"I did it for our president and our flag and our country," she added. "It was for fun, too. I'm glad it's over."