John Maine, the Mets’ no. 3 starter, was born in May 1981. Oliver Perez, the no. 4 starter, was born three months later. The Mets stole each in seemingly minor deals in 2006. Last year, each won 15 games and ranked in the top 20 in the National League in earned run average: This year, they could make the difference between a team that rates among the best in baseball’s weaker league, and a team that rates as the best in baseball. If they pitch as well as they did last year, the Mets will probably win the division. If one does and the other raises his game, they’ll almost certainly win it. If both find a new level, they might win 100 games.

Maine and Perez are, in many ways, the exact same pitcher. Both are tall and almost gawky with awkward deliveries. Both rely on 93-mph fastballs that they can throw a bit harder as circumstances require. Both throw sliders. Both are fly ball pitchers who strike out well more than twice as many batters as they walk, and and both fan about 22% of the batters they face. Both average around six innings per start. Neither has ever pitched 200 innings in a season. Both are inconsistent, unusually prone to either dominate a game or get shelled.

The main difference between them — more important than the fact that Maine is right-handed and Perez left-handed, or that Maine throws a change-up and Perez doesn’t — is in their contracts. Maine isn’t even eligible for salary arbitration until next year, while Perez will be a free agent in October, and likely able to command at least $15 million a year if he pitches even as well as he did last season. The other difference is that for all their similarity, Maine is a better pitcher.

These are two important differences, probably important enough that the two shouldn’t be classed together quite so freely as they usually are. Maine is simply more valuable to the Mets than Perez is, and unless Maine is hurt, he’s likely to remain so. Perez’s 3.56 ERA last year was quite a bit better than Maine’s 3.91 mark, he has better stuff, he’s left-handed, and in 2004, he had the best season either pitcher has had, striking out 239 men — all of this is true. It’s also less significant than it seems. Last year, for instance, while Perez’s sparkling ERA placed him 9th in the league, Maine was clearly the better pitcher, mostly because he didn’t give up huge numbers of unearned runs. When you account for the runs that were charged to the fielders, Maine gave up 4.24 runs per game, and Perez 4.56. (The league average overall was 4.71.)

Stamina is another contrast between the two. Maine made three more starts and pitched 14 more innings, but that’s just part of the story. On four days’ rest, Perez gave up a 4.79 RA, to Maine’s 4.89, and on six days’ rest, Perez beat Maine 2.29 to 3.64. The significant difference was in their performance on five days’ rest, when Maine’s RA was 3.80 and Perez’s was 4.90. In his career, Maine’s RA on five days’ rest is 3.86, against Perez’s 4.14.

Unfortunately for Perez, who pitches better the more rest he gets, starters — especially those who aspire to $15 million annual salaries — need to pitch on five days of rest as often as they do on four. This isn’t a problem Perez can’t solve, but until he shows that he can consistently pitch as his best without extra rest, it’s best to assume that he can’t.

Past this, and despite the similarities in their performances last year, Maine is likely to do better than Perez this year. Using a simple Marcel projection, which weights the last three years’ statistics and regresses them to the league average, Maine projects for a 3.98 ERA, and Perez a 4.56. Part of this is Perez’s poor performance with Pittsburgh in 2005 and 2006, and part of it is that unlike Maine he’s been historically wild. He projects to put 13% of batters faced on base via walk or hit batsman, for instance, against Maine’s 9%.

Essentially, Perez wasn’t quite as good as he looked last year, and his record doesn’t quite support the idea that he’s even as good as he was last year. Maine, meanwhile, was about as good as he looked last year, and has been so for some time. There’s a clear, meaningful distinction between them — Perez is a solid no. 3 starter with an upside well past that, and a good chance of reaching it; while Maine is a no. 2 starter who just needs to add some innings. Take into account that Perez will probably earn more over the next two years as Maine will over the next three, and it’s clear which is a terrific young pitcher and which is one of the more valuable properties in the league. You can root for both pitchers, but if you have to pick one, make it Maine.

tmarchman@nysun.com