The reception last night given by Secretary of State Alexander M. Haig Jr. and his wife Patricia may be the first Washington party ever to celebrate the official opening of a powder room.

The 475,000 powder room suite, "the Martha Washington Ladies Lounge and the Dolley Madison Powder Room," surely are the poshest facilities in the State Department, if not in the country.

The suite -- part of the diplomatic reception rooms -- is not what you would call an authentic 18th-century outhouse, or "necessary."

Though the rooms are currently named after first ladies, Clement D. Conger (White House curator and chairman of the State Department Fine Arts Committee overseeing the project) noted that if anyone would like to pick up the entire tab, "the name could be changed to commemorate the donor." For the lavatory room, alone, it would take a donation of $100,000. No price was given for the toilet room.

The suite and the rest of the diplomatic reception rooms were designed by the late Edward Vason Jones of Albany, Ga. The elevator lobby was named after Jones last night.

Conger once said that he began the effort to remodel the entertaining rooms of the State Department when, soon after the building was completed in the late 1950s, he and Mrs. Christian Herter, wife of the then-secretary of state, walked through. "And she sat down in the ladies' lounge and cried, 'It looks like a whorehouse.'"

Now the ladies' loungs entry has an American Queen Anne entrance area in the Palladian tradition as practiced in 18th-century Newport, R.I. The corner cabinet is from 18th-century Connecticut. The windows have been made smaller with blue silk damask lambrequins. The chandelier is 18th-century English. Semi-antique Chinese rugs soften the mahogany floors. 1The other furniture is American Queen Ann (circa 1720-1755).

The Dolley Madison Powder Room is furnished with American Sheraton furniture from early 19th-century New York by Duncan Phyfe.The lavatory room itself has a marble floor with a sunburst surrounding an octagon. The washstands are gilt bronze and marble with porcelain decorated bowls.

The toilet room has been designed in the American Federal style with gray-white King of Prussia marble on the floor and almost black marble on the walls.

Male guests were invited last night to view the first three rooms of the suite, to the consternation of some of those using the fourth room.

The 1,100-odd guests (many more than usual at the annual event to thank donors and lenders to the collection) at last night's buffet had to make their way past a group of pickests singing peace songs and carrying placards reading "Stop U.S. Aid to El Salvador." Once inside, the guests dined on blinis with caviar, tempura kebabs, pita sandwiches, oysters, crabs legs, and chocolate, strawberry or blueberry crepes with whipped cream.

Vice President Bush and his wife Barbara welcomed the guests along with the Haigs and Congers.

Conger said $945,000 in funds and antiques, including more than 70 gifts, were given to the rooms last year. The Fine Arts Committee spent $1,100,000 on the remodeling and acquisitions. Conger urged the guests to look at the life portrait of Thomas Jefferson by Thomas Sully (1821), recently bought for $220,000. Conger is looking for a public spirit to pick up the check. All the architectural changes and antiques furniture are paid for by individual donations.

Among the gifts recognized last night were: a carved Chippendale circa 1774 mahogany highboy, valued at $137,500 given by Mr. and Mrs. O. Ray Moore of Atlanta, and a portrait of Winthrop Sargent by Gilbert Stuart (valued at $100,000), given by the Morris and Gwendolyn Cafritz Foundation.

Secretary Haig noted the presence of presidential counseler Edwin Meese, and Cabinet members Caspar Weinberger, John Block, Raymond Donovan and Terrel Bell.

Not all those present were Republicans. Former U.S. senator and ambassador to Japan William Fulbright and fomer congressman, now president of the New York University, John Brademas and his wife were on hand.