Rosalynn Carter will wear something old, something new and several things blue during the festivities surrounding her husband's inauguration. Mrs. Carter's press office said yesterday.

Something old is the blue chiffon dress made for her by Mary Matise, then the designer for Jimmae, which she wore to the inaugural party when her husband became governor of Georgia.

Something new is the ice-blue hooded wool cape by Dominic Rompollo that she will slip on as she dashes between the six inaugural parties.

Also blue, and also by Dominic Rompollo, is the teal-blue wool jersey dress and matching coat she will wear for the swearing-in ceremonies. (There is also a huge fringed matching wool stole.) The designer calls the color "Rosalynn green."

Two additional outfits have been selected, but at the moment just when they will be worn is undecided.

Jerry Silverman has made for Mrs. Carter an almond green Ultrasuede wrap coat and a dress in wool jersey in the same color. "I had to send to France to get a perfect color match," Silverman said.

Mrs. Carter has yet to have her final fitting for a navy wool jersey dress with matching braid trim by Dorothy Farbo of Mignon, said Jack Moses, owner of Jasons in Americus, Ga., where Mrs. Carter has bought many of her clothes. Mignon was a favorite source of clothes for President Nixon's daughters, Tricia Cox and Julie Eisenhower, while they were in the White House.

The green costume by Silverman, however, was ordered through A. Cohen, an Americus department store where President-elect Carter also orders his clothes.

Although press aides to Mrs. Carter will not confirm it, Rompollo apparently has mada several other outfits for the First Lady-to-be, including an evening dress with black bodice and white faille skirt, trimmed in green ribbon, and a capelet costume.

All of the designers tapped by Mrs. Carter make tasteful clothes in the middle to better price range. The designs are more conservative than trendy.

Selections were made from sketches done by the designers at the request of Jasons and Cohen in Americus, and then presented to Mrs. Carter for her decision. Only Dominic Rompollo has been to Plains, Ga., to personally help Mrs. Carter with her clothes.