Sotheby's said it borrowed $250 million and cut guarantees it will offer sellers for the rest of the year by one-third as global economic turmoil threatens the bull market for trophy art.

In a filing late yesterday with the U.S. Securities and Exchange Commission, Sotheby's said it sought the money from Bank of America Corp. ``as a defensive step to ensure additional liquidity in response to the recent turbulence in the global financial markets.''

Its cash on hand of $290 million ``was more than adequate to meet our needs,'' Sotheby's spokeswoman Diana Phillips said in an e-mail. The additional money ``puts us in a very strong position'' during the current crisis.

The largest publicly traded auction house said it reduced guarantees to $306.1 million on Oct. 10 from $458.5 million a year ago. Sotheby's didn't put up all the money itself. It increased guarantees from undisclosed third parties by almost 10-fold to $63.3 million this month from $6.8 million a year ago, according to filings.

Sotheby's described those guarantees in yesterday's filing as ``risk-sharing arrangements with unaffiliated partners.''

At its Impressionist sale in New York next month, Kazimir Malevich's 1916 ``Suprematist Composition'' is expected to fetch more than $60 million. The Malevich will carry a new ``irrevocable bid'' symbol in the catalog. That indicates a third-party guarantee, in which an external guarantor provides the first bid on a lot at auction.

``If there's only one bid, then the guarantor buys the work at a price that includes premium,'' said Matthew Weigman, a London-based Sotheby's spokesman. ``If the work sells for more, the guarantor gets a cut of the upside.''

Sotheby's shares have plunged 78 percent in the past year, compared with a 36 percent drop in the Standard & Poor's 500 Index.