WHEN the King and Queen of Sweden swept into Washington, they checked their crowns at the National Gallery of Art. King Carl XIV Gustaf and Queen Silvia of Sweden brought with them a priceless collection of ruby- and diamond-paved crowns as part of ``Sweden: A Royal Treasury 1550-1700,'' an exhibit that has just opened at the gallery. The collection's 100 baroque objects include everything from a royal mousetrap to a gold coronation costume.
The royal couple also appeared, crownless, at the National Portrait Gallery. He wore a gray pin-striped business suit, she a regal purple silk dress with pearls, to open the exhibition ``Masterpieces from Gripsholm Castle: The Swedish National Portrait Collection.'' Both exhibits saluted the beginning of a year-long celebration across the United States of ``The Year of New Sweden,'' marking the 350th anniversary of the first permanent Swedish colony in North America.
``Dazzling'' was the word used by National Gallery director J.Carter Brown to describe the Royal Treasury exhibit. Mr. Brown refused to discuss the value of the priceless collection, as a matter of National Gallery policy. He admitted, though, ``It is a subject that's going to pop into people's heads, because of the dazzle. But that simply is the wrong emphasis, in our view,'' for these ``irreplaceable cultural objects.''
The exhibit is, however, known to be dazzlingly insured. The show's curator, Michael Conforti, noted that the insurance cost ``of these large-scale international exhibits is very high, and valuing [any of] the crown jewels is a very abstract sort of thing. Do you put $2 million? Do you put $10 million?''
Among the dazzlers is the sumptuously beautiful crown worn by Queen Maria Eleonara in 1620, then in 1650 by Queen Christina, whom Garbo played on screen. The massive gold crown, cobblestoned with violet-red rubies and diamonds, has a cap of red violet satin encrusted with gold and precious stones. It is topped by a blue orb and diamond cross.
There is also a somber crown of gold and black velvet decorated with black and white enamel, smoky rock crystals, and pearls; it was part of the burial regalia of Charles IX in 1612.
This show is the first one the gallery has done specifically about royalty, unlike its hit ``The Treasure Houses of Britain,'' which featured the titled rather than the royal.
``This really focuses on how the decorative arts became part of the whole scenario of royal power in the age of the baroque,'' Mr. Brown explains. The show, set like a jewel against a background that evokes the dark gray granite walls of an ancient castle, includes armor, royal costumes glittering with silver and gold embroidery, sculpture, drawings, enamels, jeweled orbs, scepters, and inlaid firearms.
``This is the first time ever that these treasured objects have been seen in the United States, and it is also the very first time for many of the objects to go outside of Sweden,'' says Agneta Lundstrom, director of the Royal Armory, who gathered the objects together. Reporters at the show's Swedish press breakfast were reminded that some royal families, such as the British, do not allow their crown jewels out of the country.
Michael Conforti, chief curator of the Minneapolis Institute of Arts, which organized the exhibit with the National Gallery, notes that it is ``one of the most extraordinary exhibitions of decorative arts ever to be staged here in America.
``The textile collection is the most extraordinary in the world, the crown jewels among the most important in Europe, and objects from the Swedish arms and armor collection among the finest of any European national collection.''
Standing in front of a tiny mousetrap pendant from 1600, done in gold, diamonds, rubies, and pearls, he said his favorite in the collection is the ``horse d'ecor.'' These fittings for the coronation saddle of Charles IX in 1607 include saddle mounts and plume holders done in gilt silver gleaming with topaz, Swedish rock crystal, smoky quartz, and garnets.
Ms. Lundstrom finds the most precious object to be the purple and gold brocade dress, embroidered in silver and gold, that tiny four-year-old Charles XI wore, possibly to his father's funeral, as heir to the Swedish throne in 1660.
``It is important for every museum that you have the feeling this is about human beings, not only about art objects,'' she says.
As the shepherdess of the collection, Lundstrom oversaw the packing of the objects in a special polyester packing film designed to protect the objects against airplane vibrations, which might jar loose some of the precious stones. A jewel count was made before, during, and after packing in 50 large and small pine crates, some of them double boxes.
``A Royal Treasury'' will be on view here until Sept 5, and in Minneapolis Oct. 9-Jan. 1, 1989.
At the National Portrait Gallery, the King and Queen of Sweden were heralded by a royal burst of music, a fanfare composed for the occasion by Ake Peltersson and played by the Stockholm Philharmonic brass ensemble.
Before touring the show from Gripsholm Castle, the king noted, ``Portraits give you a wonderful chance to meet people from different ages, countries, and cultures.'' The castle, which dates from the 1500s, is known as the Swedish National Portrait Gallery.
The Swedish portrait collection includes some playful royal art, such as ``The Chicken Picture,'' in which Johan Pasch in 1747 portrayed Crown Princess Louisa Ulrica's court ladies as hens, with Count Carl Gustaf Tessin as a rooster crowing behind them.
The collection also includes a painting of former UN Secretary-General Dag Hammarskjold by Ben Shahn, as well as portraits of Swedish nightingale Jenny Lind, playwright August Strindberg, Nobel Prize-winning economist Gunnar Myrdal and his wife, Alva, a Swedish ambassador.
And finally, a family portrait of King Carl XVI Gustaf and Queen Silvia with their children, done by John-Erik Franz'en in a style as realistic as a Kodak photomural. This show closes July 10.