Hardy Amies, the British designer who regularly creates clothes for the queen of England and whose dresses and suits are in the wardrobe trunks of Her Royal Highness the Princess of Wales, has some simple advice on dressing for those on the current Washington party circuit.

"Of course, you want to look as pretty as possible and you don't want to be outrageous," cautions Amies. "You want to look comfortable in your clothes as if it's a dress that you have worn before and as though you meet royalty at least every other week."

That will be easy for the select group of Washington women participating in the celebration of the royal visit. "Haven't bought a single new thing for the occasion," says the scrappy Evangeline Bruce, whose late husband was ambassador to the Court of St. James and whose role is both hostess and guest in the celebration of the "Treasure Houses of Britain" exhibition at the National Gallery of Art.

American designer Bill Blass, whose designs are likely choices for First Lady Nancy Reagan, Carole Price, wife of the current ambassador to the Court of St. James, and others for the many formal events in this period, says his clients have chosen "just the most becoming and most glamorous."

Blass isn't sure if black would be appropriate at parties attended by the Waleses but, in fact, there won't be any royalty at many of the parties, but even then, it wouldn't be a problem. "One wears it now at Windsor and Buckingham palaces," says Bruce.

Most women attending several occasions will pair up the dress and the event at the last minute, says Blass, and Carole Price agrees. "There isn't much time to work out those things until the last minute. And sometimes weather makes a difference," she says. Most of her clothes will be from American designers, "except a few French things from the old days," says Price, laughing.

Pamela Brown, the wife of J. Carter Brown, director of the National Gallery, was in New York this week, attending the New York Horse show to see a horse she'd raised. She planned on making a last minute choice, before Thursday's opening gallery dinner, between dresses selected from the shop Marie Martine in Paris or a gown by Pauline Trigere. She chose the Marie Martine.

Jo Carole Lauder, whose husband has been traveling, couldn't resist the yellow and black Arnold Scaasi design she saw in the window of a New York shop to wear during the current week of events. Lauder admits she may have to wait to wear it -- depending on the travel schedule of her husband, the deputy assistant secretary of defense.

Not all the events surrounding the royal visit are in the evening and, according to designer Amies, hats and gloves are really the thing to wear. "Rules apply here in England," says Amies, adding quickly, "but even here people make their own rules. Don't think anyone is going to be affronted if you show up without a hat."