The unexpected appearance of two rival bidders at a bankruptcy sale has forced the owners of a Washington shopping center chain to pay nearly $1 million more than expected to buy back a half interest in the firm.

After a tense day of bidding in federal court in Baltimore Tuesday, Combined Properties Corp. agreed to pay approximately $5 million for 399,000 shares of its stock that were owned by the estate of the late Leo Goodwin Jr., it was learned yesterday.

Combined Properties originally had offered about $4.1 million for the Goodwin stock, which represented a 46 percent interest in the shopping center firm, owner of more than a dozen local centers.

Goodwin, son of the founder of the Geico insurance company, filed for bankruptcy in 1976, listing debts of more than $32.6 million, one of the biggest personal bankruptcies in American history.

Before the complex bankruptcy proceedings were completed, Goodwin died. The court continued to sell his assets to pay off the creditors.

A few months ago Combined Properties offered to pay $9.75 per share, plus $205,000 in expenses, to buy back Goodwin's interest in the shopping center firm.

Controlling interest in Combined Properties is owned by Herbert Haft, president and chairman of the board of Dart Drug. Combined has a handful of other stockholders, most of them members of the Haft family.

Under federal bankruptcy law, the sale on the stock back to Combined required court approval and an opportunity for other bidders to top the Combined offer.

When the court hearing opened in Baltimore Tuesday, two other shopping center developers showed up -- Sidney Brown of Beltway Plaza Developers Inc. in Greenbelt and Theodore N. Lerner and Albert Abrahamson, owners of Tysons Corner, White Flint and other local malls.

Attorneys for Lerner and Abrahamson and Brown handed over the $200,000 certified checks required for admission to the auction, and bankruptcy judge Glenn J. Golbburn opened the bidding.

Lawyers and clients huddled in various parts of the courtroom, and in a series of bids, pushed the price for the Goodwin stock from $9.75 a share to $12.11. When Haft's team offered nearly $5 million -- including expenses -- for the stock, the rivals did not respond.

The bidding forced the Haft interests to pay roughly $1 million more than originally offered for the half interest in the shopping center chain and produced a windfall for creditors of Goodwin.

About $3.6 million from the sale of the stock will go to pay off a lien on the shares to Riggs National Bank. The remaining money -- including the extra $1 million -- will be used to settle with unsecured creditors.

Although the Goodwin bankruptcy is far from complete, attorneys involved in the case say creditors will get nearly 100 cents of the dollar for their debts. At the time Goodwin filed for protection under Chapter XI of the bankruptcy laws, he said he had assets of $27 million to pay debts of $32.6 million.

A prominent Washington businessman who used his father's stock in Geico to build his own financial empire, Goodwin was forced into bankruptcy when Geico got in financial trouble in 1975 and 1976.

The value of Geico shares plummeted from $60 a share to $4 in a matter of months, wiping out much of Goodwin's fortune and making him unable to repay debts secured by the stock.

Goodwin's shares in Combined Properties have been under the supervision of the bankruptcy court since 1976. By outbidding the other shopping center owners for the Goodwin shares, Haft and his associates in Combined kept themselves from getting an unwanted partner.

Combined owns 17 shopping centers, one in Florida and the rest in the greater Washington area. They include the Bradlick, Fair City, Rolling Valley and Virginia Plaza projects in Virginia, the White Flint Plaza adjacent to Abrahamson and Lerner's White Flint Mall, and several smaller projects.