Joy Dirksen (Mrs. Howard) Baker gave two parties last night -- at the same time but at some distance from each other.

"I can only stay for 15 minutes," she said at the opening buffet benefit of the Washington Hilton Hotel Antiques Show for the Christmas Seals District of Columbia Lung Association. Baker chaired the event, planned long before the election.

"I have to be across town at the Library of Congress, where we're giving a dinner for the President-elect and Mrs. Reagan and the senators. Howard and I have to be in the receiving line," she said. Her husband is expected to be majority leader of the upcoming Republican Senate.

Baker said she planned to come back to the antiques show today -- and not just for a ceremonial visit. "We've just remodeled our house and I need a French country armoire to hide the television set and the stereo in the living room."

Baker paused long enough to ask for the name of a repairman for her grandfather's music box. Another Republican, Gilbert Hahn, and his wife, Margot, stopped in before another dinner. "You're back in style again," someone called to Hahn, but his wife said, "He is -- I'm out, I'm a Democrat." "That's all right," her husband said. I'll take care of you."

Though Baker left early last night, the 225 other guests, who paid $35 each, stayed until 10 p.m. to browse through the booths of 90 exhibitors from 16 states. Seventeenth- through 19th-century furniture, porcelain, pewter, silver, quilts, candlesticks and more attracted the treasure-hungry crowd. The fall antiques show is different from the Older Washington Thrift Shop show concentrating on 17th- and 18th-century objects, which will be held in January, opening with a sit-down dinner.The Hilton show has a broader range of antiques, including less expensive 19th- and even early 20th-century objects. Diane Wendy of Rye, N.Y., producer of the show, said that there was less silver and 20th century art in the show than last year. "We're trying to bring in what people from Washington want. Washington has very sophisticated buyers."

Jan and Larry Malis had political ribbons from the 1892 Benjamin Harrison campaign at $55 to $85.

Nathan D. Cusham of Yarmouth, Maine, had the most Art Nouveau silver, including silver-on-glass pitchers. Quilts were all over the show. An abstract purple, red and green design from an Amish community was offered for $3,800 by the All Of Us Americans shop of Bethesda.

The show is open from noon to 10 p.m. today through Saturday and from noon to 6 p.m. Sunday. Admission is $3. Adam Weschler will conduct appraisals tomorrow and Saturday from 6:30 to 8:30 p.m. for a $3 donation to the D.C. Lung Association. Gloria and Robert Speert will talk about Oriental rugs at 2 p.m. tomorrow at the show.