It was an odd place for 63-year-old Claudia Alta Taylor Johnson to be making her stage debut, but there she was, appearing with the Winnipeg Symphony in Grand Forks, N. Dak. (pop. 43,000), and looking uncharacteristically nervous about it. "I'm uneasy," she confessed before the curtain, fretting needlessly over whether her necklace would rattle against the mike. "Very uneasy."

For its tribute to America's Bicentennial, the Winnipeg Symphony had tried to enlist both President Ford and Prime Minister Pierre Trudeau. When that grandiose scheme fell through, symphony managers turned to Charlton Heston, who has played Moses, Michelangelo and John the Baptist. Alas, film commitments forced Heston's withdrawal. Then the call went out to Lady Bird in Austin, Texas. "I was shocked and amazed," she said. "I really regard myself as a musical illiterate."

Lady Bird was offered $10,000 for three dates. The money will go to one of her most cherished projects: the LBJ Memorial Grove in Washington, a 15-acre white pine forest on an island in the Potomac. "It will cost $2 million, and we're three-quarters of the way there," she explains animatedly. "It's a lovely quiet green place with a view of all the Washington landmarks."

Before an audience of 1,440 that half-filled Grand Forks' Chester Fritz Auditorium, Lady Bird, attired in a long black evening gown, recited four passages. She began with excerpts from the Declaration of Independence, then went on to deliver the narrative of Aaron Copland's A Lincoln Portrait and William Schuman's New England Triptych. She finished up with portions of LBJ's Great Society speech. Her performance won her a thunderous standing ovation. Two succeeding appearances in Winnipeg, Canada brought further kudos. "The Yellow Rose of Texas blooming on the Frozen Prairie," gushed one observer. "She is," commented delighted maestro Ruben Gurevich, "a natural performer."

She was cosseted and escorted by nine Secret Service agents. Yet Lady Bird does not pine for the glamour of the old political days. "That was Lyndon's life," she recalls, "and when we were in it, I shared it. But with his death I decided I'd do my own thing."

Her own thing includes service on the Board of Regents of the University of Texas (she is class of '34, Journalism), as a trustee of the National Geographic Society and as an adviser to the National Park Service. She is active in the LBJ Company, which has interests in radio and TV. Above all, she visits her five grandchildren as often as possible. (Her younger daughter, Luci Nugent, is expecting her fourth child next month.) "When we were in the White House we never had enough time for that," she says. There were, however, a few relaxed moments. "When you got out of the elevator on that second floor of the White House," she remembers, "you felt like you could kick off your shoes and be at home."

She has a great sympathy for First Ladies. "They are what they are," she says. "Each one is different and not elected or chosen by anybody except one man." She feels loyalty also to their husbands and found exposés of President Kennedy's sex life distressing. "I knew, liked and respected him," she says. "I do not think well of reporting on it."

She also did not think well of the concert program's description of her appearance as a world stage debut. "That implies a career that will go on in the future," she says. "This is strictly a one-time event." Still, it was an experience she clearly had relished. "I know how Lyndon would feel," she explained in Grand Forks with a smile. "He would be laughing and proud. He always wanted me to try new things."