The debate over this year’s American League Most Valuable Player award takes on something of a theological tenor. On the one hand, you have Boston’s David Ortiz, the most feared batter in the league, an awesome power hitter who’s hit a preposterous number of dramatic, game-winning home runs this year, solidifying his reputation as the game’s best clutch hitter. On the other, you have the Yankees’ Alex Rodriguez, who’s been workmanlike in putting together one of the great hitting seasons in New York history.

This one has it all: Boston against New York, Ortiz’s genuine charisma against Rodriguez’s synthetic version, debates over whether clutch hitting really exists and whether the designated hitter is even a real player.

As is, no matter the outcome of these arguments, this weekend’s showdown for a playoff spot will determine not only the pennant winner, but the MVP as well. Barring flag-winning heroics from Ortiz, though, I think Rodriguez should have this one nailed down.

It’s certainly close, though – closer even than I would think possible between someone who plays every inning and someone who plays a non-position. You can count me as a DH-hater both because the idea of a half-player is aesthetically offensive and because even the best DHs are a lot less valuable than people realize. I think of it like this: The worst a defender can realistically be without his team taking him out of the field is about 20 runs below average, territory inhabited by Bernie Williams or Mike Piazza at their nadirs.

A DH, because he provides no defense whatever, is by definition worse than that, and so when judging his value, one starts with an enormous handicap. Twenty runs is a lot – that’s about the difference between Gary Sheffield’s bat and that of Kansas City right fielder Emil Brown this year.

So, after comparing their hitting statistics, it would seem absurd to even compare Ortiz and Rodriguez. The Yankee is hitting .320 BA/.424 OBA/.607 SLG with 18 steals in a tough park for right-handed hitters; the Boston DH is hitting .295/.397/.602 with one steal in Fenway. In total, the various formulas that measure runs produced credit Rodriguez with around 140 and Ortiz with around 130, without taking into account that Rodriguez has used seven fewer outs. One would need to be generous to Ortiz to say the two have equal numbers this season, and since Rodriguez brings defensive value as well, this shouldn’t even be something one has to think about.

There’s more to offensive performance than just numbers, though; there’s also context, which is where Ortiz’s argument resides. Using crude measures of clutch performance, A-Rod has been respectable, with a .961 OPS in close-and-late situations and a .941 mark with runners in scoring position and two outs. But Ortiz has been a monster, with a 1.238 OPS in the former situation and a 1.214 mark in the latter.

Add in the perception that Rodriguez has piled up the numbers in blowouts (which he has – 20 of his 127 RBI have come in three games the Yanks won by a combined score of 54-15) while Ortiz hits when it counts (which he has, with a well-noted series of game-winning home runs that have kept his team in the race),and there is a strong case to be made that Ortiz has been the more valuable hitter.

In fact, an interesting article last week by James Click of Baseball Prospectus showed the margin is a lot wider than people might think. Since the 1960s, number-crunching baseball fans have known that one way to measure player value is to gauge the amount by which each of his at-bats has changed the probability that his team would win the game. By this method, a two-out double with the bases loaded in the bottom of the ninth with your team down by two counts for a lot more than your 10th RBI in a 17-run massacre.

Because it’s so dependent on a hitter finding himself in situations where he’ll have a chance to affect his team’s fortunes, this isn’t the best way to judge how well a player is likely to do going forward. But in terms of judging a player’s value retrospectively, it’s a pretty powerful tool. Click, using play-by-play data, found a stunningly large advantage for Ortiz, who led Rodriguez (second in the league by the measure) 7.12 wins to 4.59 wins. That margin is probably larger than the difference between Ortiz’s non-defense and Rodriguez’s defense, actually, and makes it clear that Ortiz’s partisans aren’t just worshipping the false god of the RBI.

Why, then, do I support Rodriguez anyway? A few reasons. First, the win probability method isn’t particularly transparent (to me at least), and while the results in this case sound about right, were I to base an opinion on it, I would be doing so not merely on the basis of a number, but one I’m not entirely confident in.

Second, while there’s no doubt Ortiz has been better in the clutch, and deserves a lot of credit for that, it’s hard to separate out how much of that is a matter of opportunity. I’m not comfortable with giving A-Rod demerits because the Yankees didn’t find themselves in as many games that were tied in the bottom of the ninth – the fact that they didn’t is actually a point in their best player’s favor.

Finally, no matter how you massage the numbers, a DH isn’t a full-time player, and it isn’t hard to find someone who can hit, while it’s awfully hard to find someone who can hit like an MVP and play 150 games at third base. Jason Giambi and Cleveland’s Travis Hafner are quite comparable to Ortiz; there’s no one, really, who’s comparable to Rodriguez, and that makes a big difference. In any event, the winner of this race is going to be the one who plays on the team that wins this weekend, and should either player have a big impact on that, he’s going to deserve his trophies.

tmarchman@nysun.com