Joseph Hennage, one of the biggest donors to the State Department's Americana fund, announced he was boycotting the Russian blinis and red caviar.

"Afghanistan?" he was asked. "No, Scarsdale diet," came the reply.

Hardly anyone else looked to be on a diet last night at the party in the State Department's lavishly furnished diplomatic reception rooms. The 500 or so guests had helped raise $736,000 last year to remodel and furnish the rooms in the American Federal manner of Albany, Ga., architect Edward Vaso Jones. They dined on chicken satay, oysters, crab claws, Peking duck, vegetable tempura and a choice of strawberry or chocolate crepes -- all for an estimated cost of about $20,000, according to Gail Serfaty of the staff. "Most of it comes out of the State Department entertaining fund," said Serfaty. "The Fine Arts Committee pays the rest."

Clement Conger, chairman of the commettee, said $88,511.25 was spent on new furnishings, $209,132.72 on architectural improvements including the elaborate new elevator lobby. That left $439,091.99 unspent -- for the moment. Conger said he is planning to redecorate both the men's and women's lounge and then another small drawing room.

Secretary of State Cyrus Vance didn't make his party -- though he'd hoped to up until the last moment, said Conger. Instead Deputy Undersecretary of State Warren Christopher did the honors and confided that Conger has exported his idea of furnishing public places with private donations to Australia and New Zealand.

In the midst of plenty, Conger mourned those that got away. "Thirty-five percent of the furnishings are on loan. They can walk out the door the way they walked in. We lost 30 objects last year when their lenders took them back."

The biggest monetary contribution was $51,500 from former senator and Mrs. Williams Hernstadt of Las Vegas, Nev. The most important furniture piece contributed was a Chippendale Massachusetts carved San Domingan mahogany bombe chest, donated by the Hennages.

All over the rooms were discreet tags saying, "This chair available for donation, $15,000," or "This dressing table available for donation, $161,700." d