A surprise bidder, the Hotel and Restaurant Workers Union, bought Georgetown's historic Corcoran School at auction yesterday for $1.8 million. A union official said the old red brick building at 28th and M streets NW will become the union's international headquarters.

Ron Richardson, executive director of the union's Washington local, represented the international in the bidding and agreed to pay $200,000 more than the minimum price set by the D.C. government. He said the 400,000-member union decided only recently to move its headquarters from Cincinnati.

Richardson put down a deposit of $180,000 and was given 220 days to conclude the deal. A previous auction failed last year when the city sought to impose a deadline of 60 to 90 days for concluding purchase of the property. Potential bidders complained that did not allow enough time to arrange construction loans and permanent financing.

There was one other bidder yesterday, architect Royce Lanier, who had planned to restore and either sell or lease the school to another occupant.

Corcoran School, a building with 12,000 square feet on a lot of 33,000 square feet, is the largest of 27 surplus properties the city has decided to put on the market. The smallest, a 1,200-square-foot vacant lot at 304 M St. NW, was sold yesterday for $10,000 to T&T Minority Enterprises. To date, 12 property sales have yielded about $5 million.

Richardson said the building will be renovated. Part of the site may later be developed for other purposes, he said. The site is partly zoned commercial and partly residential.