More than most, the annual Washington Antiques Show is a benefit that draws old Washington. You don't see many politicians, members of the administration or even many embassy officials. These Washingtonians were here generations before the Carter crowd and expect to be here long after the current crop of ambassadors moves on to Peking.

Many of those at the black-tie preview dinner for the show at the Shoreham Americana Hotel last night came not to buy but to check out the prices to see how much their own antiques at home had gone up; they were universally pleased. Those who did come to purchase seemed largely to be adding to their collections rather than starting new ones.

The show attracts dealers who specialize mostly in the federal style suitable for Georgetown houses. You see very little of the art deco or even American Empire at this chaste show.

Last night Clement Conger, White House curator and perennial speaker at the show's young collector's night (Saturday at 6:30 p.m.) bought for himself a rare tobacco-leaf Chinese-export porcelain bowl from dealer Elinor Gordon of Villanova, Pa.

Former Supreme Court Justice Abe Fortas, his wife Carolyn Agger, and Evelyn Zlotnick, looked long and hard at the exotic jewelry of Edith Weber. The Edith Weber Shop among other things offered a bracelet of seven hand-painted eyes. In the Georgian period it was fashionable to wear the portrait of your lover's eyes. The bracelet is $2,200.

The co-chairmen of the show, Mary Jane Mockwort and Gail Matheson tried out the $7,500 carved carousel horse (Philadelphia, late 19th century) in the booth of Biher and Coger of Ashley Falls, Mass.

Last night's dinner was a benefit for the Thrift Shop Charities: the Child Health Center Board of Children's Hospital, the Children's Hospital National Medical Center, the Columbia Hospital for Women clinics, The Hospital for Sick Children and St. John's Child Development Center.

The show is open from noon to 10 p.m. today through Saturday and from noon to 6 p.m. Sunday. Verbal appraisals by antique specialists are being held today through Saturday from 10 a.m. to noon. Today is silver; tomorrow, porcelain; Friday, prints and drawings; and Saturday, brass. Friday at 6 p.m. a group of exhibitors will discuss antiques.