An "unforeseen emergency" was expected to arise last night at the State Department.

Some of the most powerful people in government planned to be on hand to deal with it: Chief Justice Warren E. Burger, Secretary of State Alexander M. Haig Jr., Treasury Secretary Donald T. Regan, Defense Secretary Caspar W. Weinberger, Attorney General William French Smith, Agriculture Secretary John R. Block, and Commerce Secretary Malcolm Baldrige.

The "emergency" was the annual State Department Fine Arts Committee reception for about 500 patrons of the arts, and for at least the past 10 years, more than half the tab has been paid with money from a confidential State Department fund set up by Congress for "unforeseen emergencies arising in the diplomatic and consular service."

The elaborate reception, which is expected to cost more than $20,000 this year, was given by the committee for those who donated cash and furnishings to decorate the State Department's reception rooms for visiting dignitaries.

"This business of the care and feeding of the donors and lenders is what made this project the success that it is," said Clement E. Conger, curator of the diplomatic reception rooms and of the White House. "It's worth every dollar that goes into it because of the contributions it produces."

This year's menu included oysters and clams, international foods prepared individually at buffet stations, and flaming crepes filled with strawberries and blueberries.

Since the project began in 1961, Conger has collected $25 million in art objects, a quarter of which are loaned. Among the 3,000 pieces are the desk used for the signing of the Treaty of Paris and a desk designed by Thomas Jefferson.

Last year alone, Conger raised more than $1.4 million in cash contributions and another $1 million in furniture and early American art objects for the rooms, which are located on the top floor of the State Department. The State Department reimbursed the Fine Arts Committee $18,500 for that reception, which cost a total of $33,727, according to the committee's staff assistant, Patricia L. Heflin.

"That [payment for the receptions] is the only reimbursement we receive from the State Department," Heflin said. "The only reason it comes from the emergency fund is we have no appropriated funds."

In 1980, the State Department paid $15,000 of the $21,000 tab, and Conger said he expects the emergency fund to cover more than half of this year's reception.

Asked why donations could not cover the entire cost, Conger said, "It could be paid by donations but I don't think it should be because often when people give money it's for acquisitions."

When Under Secretary of State for Management Richard T. Kennedy was asked how expenditures for the annual receptions qualify as "unforeseen emergencies," Kennedy said in a letter that the collection in the rooms represents a "national treasure" that reminds foreign visitors of America's history and cultural heritage.

"As such," Kennedy said, "the department's contribution toward the cost of an annual reception to express appreciation to those dedicated people who contribute so much to seeing that our diplomatic and official facilities do the United States credit very much furthers U.S. foreign policy objectives."

Under the 1956 law that established the emergency fund, the secretary of state is authorized to determine what expenditures qualify for payment by the fund. He is not required to give an accounting of his use of the money.

In the last fiscal year, Secretary of State Haig had a $4 million emergency fund budget; for fiscal 1983, the Reagan administration is proposing to increase that figure to $4.5 million.

The State Department said the fund generally is used to cover emergency evacuations, travel by the secretary of state, foreign trips of the president, vice president and congressmen, and domestic and foreign entertaining.

"There are also some limited but highly classified expenditures directly related to sensitive foreign relations missions that cannot be disclosed in an unclassified document," the department said.

"The secretaries of state have been enthusiastic [about the fine arts project] because they see the effect on foreign leaders who come here," Conger said. "It gives a reflection of the American cultural heritage that most foreigners have no idea we have."

Last year, Conger opened a $475,000 powder room, the Martha Washington women's lounge and the Dolley Madison powder room. Like the other 12 rooms that constitute the reception area, the women's lounge is designed and decorated to reflect accurately American furnishings between 1740 and 1825.

The lounge has an American Queen Anne entrance in the Palladian tradition as practiced in 18th-century Newport, R.I. The windows have been made to look smaller with blue silk damask lambrequins. The chandelier is 18th-century English. Chinese rugs soften the mahogany floors. And the toilet stalls are shielded by white-louvered swinging doors.

"It was so embarrassing," the 69-year-old Conger said of the bathrooms before they were redecorated. "The lounges were exactly like the ones downstairs [in the main State Department building]. Now we don't worry."