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NEW YORK (Reuters) - The St. Louis Cardinals and their slugger Albert Pujols failed to agree on a new contract by the first baseman's self-declared Wednesday deadline, leaving open the chance he will become a free agent after this season.

Pujols, a three-time National League Most Valuable Player, had said if no agreement was reached before he began spring training he would stop talks until the 2011 season ended so he could focus on the upcoming campaign without distraction.

The 31-year-old Dominican, who could become a free agent in the next off-season, was seeking a 10-year deal worth about $300 million, according to media reports.

"We made every effort to extend his contract," Cardinals chairman Bill DeWitt Jr. told reporters Wednesday at the club's spring training camp in Florida.

"We have agreed with him not to discuss it until after the season. We will revisit it again following the 2011 season, at which time we'll again make every effort to keep him."

Pujols, who has also been MVP runner-up four times in his 10-year career with the Cardinals, led the National League with 42 home runs and 118 runs batted in last year.

"We felt very good about the offer we made," general manager John Mozeliak said. "We thought it recognized his iconic status and we thought it still allowed us to put a successful club out there.

"We feel we made every effort to get a deal done."

Pujols, who will make $16 million this season, is expected to arrive at the training camp on Thursday.

The Cardinals would still have exclusive negotiating rights with Pujols, a nine-time All-Star, from the end of the season until five days after the World Series before he would become a free agent.

Pujols's agent, Dan Lozano, said the impasse does not necessarily mean the end of his career with the Cardinals.

"While both parties were hopeful that an agreement could be reached, a difference of opinion in determining Albert's value simply could not be resolved," Lozano said in a statement.

"The expiration of today's deadline does not eliminate the possibility of Albert returning to the Cardinals in 2012, but simply delays negotiations until the conclusion of the Cardinals' season."

(Writing by Larry Fine, Editing by Steve Ginsburg)