Following in the much-publicized footsteps of her nephew Prince Charles and other royal relatives, Princess Margaret yesterday got her own semiprivate tour of the "Treasure Houses of Britain" exhibition at the National Gallery of Art.

The 55-year-old younger sister of Queen Elizabeth browsed through the rooms of the exhibit, accompanied by five friends and J. Carter Brown, director of the National Gallery. The group chatted and chuckled over various objects as they wandered at a leisurely pace under less frenetic circumstances than those of Charles and Diana's tour last November.

"Oh, it's marvelous," the princess said of the exhibit, on her way to lunch with Brown at the gallery. "A lot of familiar things in different settings." The objects of the exhibition have been culled from the great country houses and estates of the British royalty and aristocracy.

"She is very knowledgeable," Brown complimented her.

The group started its tour in the Tudor Renaissance room shortly after 11 a.m. Brown directed the princess to the centerpiece of the room, the giant Lumley Horseman, an oak statue dating to the late 1500s. "It's actually the earliest equestrian statue known in Britain," Brown told her as they circled the statue and Brown animatedly pointed out details.

The princess and her companions, Lady Glenconner and Lord Napier and Ettrick(members of the princess's staff), British historian Sir John H. Plumb, and two other friends, Mr. and Mrs. Oliver Baring, lingered over the Rainbow Portrait of Elizabeth I. The princess, dressed in a dark green print velvet suit with a diamond brooch, carried a pair of black gloves and produced a pair of glasses that she slipped on to look over different objects. She gently laid her hand on the Sea-Dog Table, a late-16th-century walnut table, one of the most celebrated surviving pieces of Elizabethan furniture, that sits on massive carved chimeras -- dogs equipped with wings and breasts and dolphin tails.

There was another stop at the portrait of Elizabeth Hardwick, Countess of Shrewsbury, bedecked with multiple strands of waist-length pearls in what Brown described as a "drop dead necklace."

The gallery did not close off the exhibition during the princess' tour, but officials did slow the number of people permitted through. About a dozen gallery tourists hung back, taking their own tour and quietly eyeing the princess.

Before they left the Tudor Renaissance room, Brown and Margaret walked over to the 16th-century painting, "The Family of Henry VIII: An Allegory of the Tudor Succession," which just happened to be adjacent to the cordoned-off press area. The princess smiled briefly at reporters and photographers who flocked toward the side of the rope where she stood and wedged themselves into a pyramid of cameras and bodies perched precariously close to a pair of 16th-century steel and brass andirons.

Margaret, who is on a private visit to Washington, arrived Sunday and plans to leave tomorrow for New York. There she is scheduled to attend a gala performance of the Sadler's Wells Royal Ballet -- of which Princess Margaret is president -- -at the Brooklyn Academy of Music.

Other than to say she's staying at the British Embassy here, the embassy will disclose no other details about her itinerary. Asked if she was traveling with anyone, embassy press secretary John Hughes laughed and referred to the recent Washington visit of another royal husband and wife: "You should have seen the trouble I had with the press about Princess Michael of Kent," Hughes said.