AMSTERDAM - A Dutch court blocked ABN Amro Holding N.V.'s planned sale of a Chicago bank yesterday, disrupting ABN Amro's plan to be acquired by Barclays P.L.C. for $91 billion.

The court said ABN Amro must seek shareholder approval before it can sell its U.S. subsidiary, LaSalle Bank Corp., to Bank of America Corp.

The ruling was a major setback for ABN Amro's management, which had planned to sell LaSalle for $21 billion and then sell the rest of the company to Barclays, the British bank.

The ruling increases the chances that a three-bank consortium led by the Royal Bank of Scotland Group P.L.C. will win the bidding war for the Netherlands' biggest bank. The group has suggested a purchase valued at $98.5 billion.

Either bid for ABN Amro would be the highest price paid in a banking buyout.

Barclays' bid is now in limbo, because it was both preliminary and dependent on the LaSalle sale, while the Royal Bank consortium has more breathing room to make its preliminary offer official.

The court said the sale of LaSalle was so interwoven with the Barclays takeover bid that it should have been put to shareholders for a vote. ABN had argued that the deal was too small to require shareholder approval.

The court "forbids ABN Amro . . . by means of an immediate injunction . . . from proceeding with the purchase and sale of [LaSalle] . . . without previous approval given by a general meeting of shareholders," Presiding Judge Huub Willems said, reading the decision of the Enterprise Chamber of the Amsterdam Superior Court.

Bank of America spokesman Scott Silvestri said the company had "a binding contract, and intends to take all necessary steps to protect our legal rights."

ABN Amro spokesman Neil Moorhouse said the bank "notes the judgment of the Enterprise Chamber, and will study the implications of the outcome."

ABN Amro revealed the sale of LaSalle to Bank of America simultaneously with an April 23 announcement that it intended to accept the takeover offer from Barclays of $91.2 billion in stock.

Shareholders complained that the LaSalle sale was intended as a poison pill to forestall the higher bid from a consortium led by Royal Bank of Scotland, which wants to break up ABN Amro.

Barclays said in a statement that it would continue "to pursue its recommended merger with ABN Amro, which offers significant value to shareholders."

LaSalle has $113 billion in total assets and is one of the top 20 banks in the United States.