Nancy Reagan has chosen a wardrobe of red, white and blue to wear to the major festivities of her husband's second inauguration next weekend. And she has chosen the real heavy hitters, the best of the American designers, to make sure that the clothes created are appropriate, handsome and modern.

No one looking at them in the history books would have any trouble identifying them as strictly 1985 and flattering as well as comfortable for the first lady. Nowhere in history books or elsewhere will there be an indication of prices; it is a subject all the designers sidestep as a private matter between designer and client. But a woman other than the first lady putting together the basic elements of such a wardrobe would have to pay well over $25,000 for the ball gown, evening dress, and coat and dress costume.

There are no tricks and no surprises. For Mrs. Reagan's inaugural ball gown, James Galanos, the master of the beaded dress, has had his artisans spend 300 hours applying over hundreds of thousands of tiny beads to chiffon. The result is a figure-tracing gown that looks like two pieces but is one, covered in a variety of white Austrian and Czechoslovakian beads, the best available.

The dress gives the impression of having a bolero, then is snugly fitted through the midriff and marked with a beaded band over the hips, a silhouette that Galanos has been partial to in recent collections. The design of the beading is Art Deco on top and the solid beaded skirt is a vermicelli pattern, like zigzags, spotted with crystals. "Mrs. Reagan doesn't own elaborate jewelry," said the designer. "I wanted the dress to look like a piece of jewelry."

Galanos sent a sample of the beads from the dress to shoe designer David Evins to incorporate in a silk pump she will wear a week from tonight. And he has dropped strong hints to the first lady that an appropriate hair style would be very slick and simple. During the last inaugural, Mrs. Reagan's hairdresser Julius Bengtsson did a rather tricky, upswept style that received some criticism.

When Galanos and Nancy Reagan first discussed the dress over lunch at the White House in mid-November, Nancy Reagan's only request was that the gown be white, said Galanos from New York Saturday where he was preparing for a show in which he is being uniquely honored by his peers.

Later, he showed her several sketches, but there was little question which was her favorite. According to the designer, she was very pleased with the actual dress. She may well wear it after the inauguration, since there is no tradition of second inaugural gowns being turned over to the Smithsonian.

Although the gown is almost plastered to the body without even a pocket to interrupt the line, Galanos is not concerned that the first lady will have trouble moving among the nine balls. He's put a deep slit in the hem to make her movement easier. "But I can't remember where I put the slit," admitted Galanos with a laugh.

Bill Blass had comfort in mind when he chose the Chinese red draped silk gown for Mrs. Reagan to wear while watching the Presidential Gala Saturday night at the Convention Center. "It is both fitted and flowing so she can sit all evening without looking crushed," said Blass, who described the fabric for the slim, side-draped dress with modest shoulder pads as a heavyweight silk.

Blass had designed the black velvet and silk gown Mrs. Reagan wore to the gala four years ago, a dress that is now part of the collection of first ladies' gowns at the National Museum of American History. That dress had a dropped waistline and full skirt, which was popular at the time and would still look appropriate today. But this time the designer and client opted for a more soigne' style. "She looks well in anything proportioned to her," said Blass. He also made a wool jersey shawl in the identical red to keep her warm in the car and during the dash to the building.

Mrs. Reagan will wear matching pumps with her red Blass gown. Blass sent jewelry designer Kenneth Jay Lane a swatch of the fabric to design the costume jewelry, which Lane said, on Friday, he had not quite finished. The red turned out to be a challenge to Lane. "It's not a ruby red, in fact it is not the red of a stone. And it is not tomato red, but more a Chinese red, a lacquer red," he said.

The jewelry will be a choker -- Lane already has Mrs. Reagan's measurement -- "and something ladylike, maybe with an American eagle clasp." But the necklace will not be red. "I don't want to disturb the color of the dress," Lane explained. He has made no effort to make the jewelry look particularly real. "I don't think Mrs. Reagan particularly cares," said Lane. (Lane has made much of the jewelry for Mrs. Reagan that has been confused with real stones.)

He plans to combine twisted pearls and faux emeralds, and lightweight clasp earrings that will incorporate both, he said. "Not so lightweight that they won't show up well on television. But they won't overwhelm Mrs. Reagan either," said Lane.

Mrs. Reagan chose an electric blue coat, dress and hat by Adolfo to wear to the public swearing-in ceremonies next Monday. Press secretary Sheila Tate yesterday quoted Mrs. Reagan as saying she "picked blue because that was the color that lit up on the television screen as each state went for the president on election night."

The style of the unfitted dress and coat are appropriately serious, even official, with the details of epaulets and gold buttons. The chain belts for each are Adolfo signatures, looped through for the occasion with blue satin ribbon. The roller-brim hat was a big hit with the spring collection that he showed in New York this week. "It's a little roller off the face with the hair worn out a bit. The ladies loved it," said Adolfo, who was in Palm Beach yesterday preparing for a benefit show. Adolfo has sent along the gold-link necklace and earrings used in his spring show to wear with the outfit.

Adolfo won't show the outfit he had made for the inaugural when he repeats the showing of the spring collection here on Valentine's Day for the benefit of the Heart Fund. "It is for Mrs. Reagan alone," he said.

That leaves only one surprise in Mrs. Reagan's inaugural wardrobe. Galanos has made two cover-ups for the first lady to wear to the inaugural balls over her beaded dress. One is a white mink blouson that is shaped to rest perfectly on top of the jeweled hip band of her gown. The other is a double-faced white wool evening coat with three large jeweled buttons that close the coat to one side, long sleeves like a those on man's coat and a draped scarf for the neck.

Which will she wear? Even her designer doesn't know for sure.