The council approved the plan 6-4 but the measure must be approved a second time to become law, reports USATODAY.com.

The agreement between the district and MLB requires the council to act by December 31 while baseball owners must vote by Monday.

"We're happy that the vote was to approve," said John McHale, an executive vice president in the commissioner's office and a member of baseball's relocation committee.

The deal signed in September by the Expos and Washington Mayor Anthony A. Williams did not contain a cap.

McHale said baseball had not yet received the text of chair Linda Cropp's amendment and would wait until seeing the exact wording before responding. "I'm sure that will be a subject of discussion among our relocation committee (on Wednesday)," McHale said.

Cropp's amendment, offered during more than seven hours of debate, calls for Washington's chief financial officer to produce another estimate of the project's cost in six months.

If it is more than $100million above the current $530 million estimate, the ballpark would have to be moved to a less costly site than the one south of the capital, agreed to by Washington and the Expos, who would be renamed the Nationals.

Williams told the council he is willing to work on a funding cap and private financing for the stadium.

Cropp has also proposed an amendment that would require Washington to invite and consider private financing proposals. That, too, was approved. She said officials were already talking to potential buyers of the team who may be willing to provide stadium funds.

The agreement signed by Williams and the Expos estimates it will cost $435million to acquire land for a 41,000-seat ballpark along the Anacostia River, construct a stadium and refurbish RFK Stadium, where the team would play for at least three seasons.

Under terms of the deal, team owners will get to keep all concession, advertising and parking money generated from baseball games at the ballpark.

Williams contends the bulk of the costs will be covered by an additional gross receipts tax on businesses that gross more than $4million annually. In addition, the legislation calls for a 10 per cent tax on tickets sold to baseball games at the new ballpark as well as at RFK Stadium, where the team is to play starting in April.

There would also be a 10 per cent tax on sales at the ballpark, and a 12 per cent tax on parking there and at RFK games.