The Phillies appeared close last night to acquiring ace pitcher Roy Halladay in a stunning three-team trade that would cost them their own ace, Cliff Lee, and a potential future star in an attempt to return to the World Series for years to come.

But one baseball source told The Inquirer that a deal was not quite complete. With so many components - a potential contract extension for Halladay and a medical review for all players involved - the trade might not be finalized quickly.

Multiple sources said yesterday that Halladay and his agent were in Philadelphia engaged in what were presumably talks regarding an extension that would be an essential component of the trade. ESPN reported that Halladay was in line to receive a three-year extension worth about $60 million, with vesting options that could lengthen the deal.

Published reports last night identified various potential permutations of the deal-in-progress. According to several reports, the Phillies would send World Series star Lee to the Seattle Mariners.

The Blue Jays would receive prospects from the Phillies, identified in various reports as outfielders Michael Taylor and/or Domonic Brown, catcher Travis d'Arnaud, and, according to a csnphilly.com report, former No. 1 pick and highly regarded starting pitcher Kyle Drabek.

Seattle would send top pitching prospect Phillippe Aumont to either the Phillies or Toronto.

Phils general manager Ruben Amaro Jr. did not return a phone call, and team president David Montgomery said that he "could not comment."

Halladay's arrival in Philadelphia indicated that he was close to becoming a Phillie. Contract negotiations are typically initiated when a trade is nearly complete. Halladay, 32, has one year left on his contract, which would pay him $15.75 million in 2010. Lee will also become a free agent after this season.

Lee's agent, Derek Brauneker, flew to the winter meetings in Indianapolis last week specifically to discuss a contract extension with the Phillies. "We had a positive dialogue," Brauneker told The Inquirer yesterday. "All of the dialogue has been very positive on both sides."

But the Phils must have calculated that re-signing Lee at an affordable rate would be difficult, and decided instead to move him for Halladay. Lee will earn $9 million next season, and the Phils have long maintained that they would need to clear payroll space in order to afford Halladay.

As of last night, Brauneker had not heard from any of the teams involved in the potential deal. "He is obviously aware of the situation," Brauneker said of his client. "There must be something to it."

As if Lee would be disappointed to leave Philadelphia, Brauneker said: "He certainly enjoys being in Philadelphia. There was not much for him not to enjoy."

The Phils acquired Lee on July 29 from the Cleveland Indians for prospects Lou Marson, Carlos Carrasco, Jason Knapp, and Jason Donald. The pitcher went 7-4, with a 3.39 earned run average for his new team during the regular season, before contributing a magnificent postseason performance. In five playoff starts, he was 4-0, with a 1.56 ERA.

As good as Lee is - he won the American League Cy Young Award in 2008 - Halladay is widely regarded as the finest pitcher in baseball. Halladay won the same award in 2003, and is 148-76, with a 3.43 ERA, in a 12-year career. Last season, he was 17-10, with a 2.79 ERA.

The Phils and Jays have long haggled over Drabek and Brown. In July, Toronto asked for both players, outfielder Anthony Gose, and pitcher J.A. Happ, in return for Halladay. The Phillies countered with an offer of Happ, Taylor, Carrasco and Donald, and the talks eventually broke down. Both teams considered Brown more valuable than Taylor.

If d'Arnaud were included in this deal, the Phillies' already depleted catching depth would be further diminished. Beyond Carlos Ruiz and newly signed backup Brian Schneider, the only catching prospect in the system would be 19-year-old Sabastian Valle.

An Associated Press report said that the deal could include pitchers Joe Blanton and J.A. Happ, but there were no other indications of that.

Contact staff writer Andy Martino at 215-854-4874 or amartino@phillynews.com.