Who says fairy tales don't come true, particularly when the star of a play called "First Lady" winds up as the real McCoy 45 or so years later?

Certainly not the Congressional Club, whose 1,300 members and guests yesterday saluted Nancy Reagan at its annual spring luncheon for the wife of America's president.

"Once upon a time there was a vivacious young lady who aspired to be an actress," began "A Fairy Tale Come True," an abridged version of a tale starring Nancy Reagan that she and others found printed in their programs for the lunch at the Shoreham Hotel.

"She went to the Girls' Latin School in a big city called Chicago," the tale continued. "And, when she was a senior, she had the leading role in her school play. The play was called 'First Lady' and the setting was our nation's capital."

Everybody knows what happened after that, but in case memories needed jogging, the club brought in actress Celeste Holm, also an aspiring actress when growing up in Chicago, to put a show biz spin on things. For Mrs. Reagan, the day's surprise was the unexpected appearance in the receiving line of her girlhood chum, Jean Wescott Marshall, of Wilmette, Ill.

"It was absolutely marvelous watching Mrs. Reagan's reaction when she saw Jean Marshall," said Doris McClory, luncheon cochair with May Mineta of California, who arranged the reunion.

Another surprise was a photo album put together by McClory showing the former Nancy Davis in the Girls' Latin athletic club, glee club, student council and junior and senior plays.

While few in the audience knew it, among the pictures was one of a Hollywood actor. When McClory, wife of former Illinois congressman Robert McClory, visited Girls' Latin in February she turned up a senior class will that left the former Nancy Davis a scrapbook filled with her screen idol's pictures.

Now it can be told: Tyrone Power -- not Ronald Reagan -- first filled that spot.

"I don't know how you come up with all these surprises!" sighed Mrs. Reagan, after club president Barbara Dickinson introduced her to the crowd that included Barbara Bush, wives of Supreme Court justices, Cabinet officers and House and Senate members.