George Washington "thought of himself as playing a role upon the stage. From his youth, he was always concerned with wearing the proper costume for his part, living in the appropriate stage set, using the correct props. He knew he was a star and he wanted to play it right," said Margaret Klapthor.

Klapthor, with Howard Morrison, is curator of the exhibit "George Washington, A Figure Upon the Stage," which opens at the Museum of American History Tuesday and continues through Jan. 7, 1983. A fine catalogue accompanies the exhibition. Remarkably enough, this is the first major George Washington exhibit by the Smithsonian.

Washington, Klapthor said as she gave a preview of the show, spoke of playing his roles in the "scenes" of life with "a perfect, unvarying constancy of character to the very last act" when he hoped "to close the drama with applause," and "retire from the theatre with the . . . approbation of angels and men."

The Smithsonian owns two of the great Washington memorabilia collections, from Martha Washington granddaughters: Eleanor Parke Custis Lewis and Martha Parke Custis Peter. Other loans have come from Mount Vernon and the White House.

The exhibit aims at giving a view in the round of the First Father -- speculating, for instance, that an early case of mumps kept him from becoming a father, except symbolically.

Sitting augustly at the exhibit entrance is the much-maligned seated statue of Washington, an 1841 work of Horatio Greenough that's often called "the naked Washington." The great man is cast in the role of Zeus about to depart for Olympus. Nearby is a much more dashing figure, a painted wooden statue of Washington carved by William Sullivan.

A portrait of Capt. Robert Orme of the British Army, painted by Sir Joshua Reynolds in 1756, shows the sort of glamor Washington wished for.

The costumes demonstrate what he had in mind: a green silk coat trimmed with silver lace, owned by Thomas, Lord Fairfax; a gilded brass gorget or necklace which Washington wore as a sign of rank in the Virginia regiment; a trim black-and-cream uniform he wore when he resigned his commission in 1783; a pair of silver mounted English flintlock pistols, and a battle sword he carried during the Revolutionary War.

Klapthor noted that after his marriage, Washington set up himself and Martha as gentlefolk: his silver-handled knives and forks from London and the Chippendale ladder-back chair from Philadelphia, the Wedgwood pottery from England, the porcelain from China. The brass double candlestick lighted the writing of his farewell address. George gave Martha the charming gold watch with both an everyday case and an elaborate enameled one.

The exhibit does not hesitate to show Washington's relation to his 317 slaves, charging that he "was rather less fond of his slaves than he was of his 'breeding Mares or Stock of other kinds.' " Yet the exhibit claims the slaves generally were treated well, as befitted Washington's image of himself.

When he became commander in chief, he was just as concerned with his image as a military man. His silver camp cup with his crest, a camp stool with a folding walnut frame and, most impressive, a tent with a peaked roof and a scalloped edge, all are in the exhibit.

What Klapthor and Morrison call the lasting image is dominated by the portrait of Washington by Gilbert Stuart, or at least by his studio, for many were made after the original. Here, too, are the walking stick given him by Benjamin Franklin, the portrait of Washington done by Rembrandt Peale in 1795, the charming John Trumbull cabinet portraits of the Washingtons in 1795, his washbowl, his water jug, his eyeglasses and, perhaps best of all, a view of Mount Vernon, 1790 or later, showing Washington, amusing "myself in agricultural and rural pursuits."

From his last years are the instruments of his doctor, an account of his death by his secretary and a multitude of mourning objects from funeral medals to mourning rings to mourning paintings, to a sweetmeat dish with a picture of his tomb.

But these sad objects are overshadowed by the image created by the exhibit. Washington still lives, as his fellow Virginian Henry Lee said, "in the hearts of his countrymen."