As you try to get your head around the Phillies' reported plan to add Roy Halladay at the expense of postseason ace Cliff Lee, the important name to remember is: Cole Hamels.

For a couple of very different reasons, Hamels is the key to understanding what's going on here.

First and most obvious, Phillies general manager Ruben Amaro Jr. is demonstrating tremendous - and likely season-determining - faith in Hamels' ability to move beyond his perplexing and disappointing season and pick up where he left off after the 2008 World Series.

But there is a deeper lesson in Hamels' 2009 struggles that has to factor into the thinking here.

A year ago, in the hearts and minds of Phillies fans, Hamels was Lee to the nth power. He was the Hollywood-cool lefthander who delivered his best performances in the biggest games of his life, winning MVP trophies in the National League playoffs and the World Series. If there was a sure thing in Philadelphia sports, it was Cole Hamels.

So how sure a thing is Lee for next year and the year after that?

Yes, he was the best trade-deadline acquisition in baseball. Yes, he helped lock up the NL East title. And yes, yes, yes, he was the Phillies' only truly reliable starter in the postseason. Lee was terrific in the first playoff run of his life and became an instant fan favorite.

But Lee is no more a sure thing next year than Hamels or, for that matter, Brad Lidge was this year. He is both human and a pitcher, which means he's susceptible to all kinds of physical and psychological frailties.

That doesn't mean the Phillies are eager to get rid of him. It would take the opportunity to acquire one of the five best starters in baseball for the Phillies to part with Lee. That is an extraordinary turn of events, yet here we are. The Phillies apparently have their choice of two former American League Cy Young Award winners.

Put them on a scale and most baseball people will tell you that Halladay is a better overall pitcher than Lee. He is bigger and stronger. He throws harder. He has a longer, more telling track record of consistency.

In a New York Times story last spring, Yankees slugger Mark Teixeira was asked what made Halladay the best pitcher in baseball.

"All his pitches start in the same place and end in a different place," Teixeira said.

The righthanded Halladay throws a cutter as well as a nasty sinking fastball that makes him a safe bet to survive at Citizens Bank Park. He has a first-rate curve and change-up and occasionally throws a slider, and has enough confidence in those pitches to throw them all anywhere in the count.

So if you had to choose one of them, Halladay or Lee, the smart money would be on Halladay. The natural question is whether the Phillies truly have to choose one or the other, and why. Having both as a 1-2 combo at the top of the rotation - with the lineup intact - would make the Phillies prohibitive favorites to go to a third World Series in a row.

Alas, in the real world there are choices to make. Amaro is not working with an unlimited payroll. And he can't just make Lee accept a long-term extension of his current contract, which expires after next season. So the choice is really between one more season of Cliff Lee or four seasons of Roy Halladay.

Back it up a bit and Amaro could be getting three unforgettable months of Lee and four years of Halladay - plus outfielder Ben Francisco and a prospect to be named - in exchange for a handful of unproven minor-leaguers. Even if the trade winds up including Kyle Drabek, it makes sense.

Amaro is able to do this because he's pretty smart, and also because the Phillies are now in position to take advantage of losing organizations forced to part with premier players. If that makes you feel a bit guilty, consider it karmic payback for the days the Phillies had to unload the likes of Curt Schilling and Scott Rolen.

Would the Phillies be better with Halladay than with Lee? Yes, at least a little and maybe quite a bit. The real issue is whether they would be good enough to win it all with Halladay rather than Lee. And the answer to that, once again, is: Cole Hamels.

With Halladay and a resurgent Hamels as righty-lefty aces, the Phillies would have as strong a 1-2 punch as anyone in baseball. Amaro would have added a superb pitcher to a team that has won a World Series (without Lee, by the way) and a pennant in the last two years.

Even if it costs him Lee, there's no way Amaro could pass that up.

Contact columnist Phil Sheridan at 215-854-2844 or psheridan@phillynews.com.