Some baseball operators know many small things, and some know one big thing. The general manager of the Mets, Omar Minaya, knows one big thing — if you can afford it, you always go for the best player on the market.

In deals involving lesser players, Minaya is often right, as he was about pitchers John Maine and Oliver Perez, and sometimes wrong, as he was about Lastings Milledge. In deals involving players who rate as the best available, though, he is nearly unerring. Pedro Martinez, Carlos Beltran, Billy Wagner, and Carlos Delgado, whatever their failings, drove the Mets within outs of the World Series two years ago and within a game of the playoffs last year.

By trading for 28-year-old left-hander Johan Santana, generally considered the best pitcher in baseball, Minaya has outdone himself. The deal will send four prospects to Minnesota so long as the Mets and Santana agree on a contract extension, likely for six or seven years, at something near $25 million a year. The deal makes them clear favorites to win the National League pennant, and gives them a young ace to match peerless young infielders David Wright and Jose Reyes.

Trading for Santana at all would have dispelled the evil funk that has surrounded the team since it collapsed down the stretch last fall; getting him by giving up what Minaya did makes for one of the great moments in team history. Much as the Atlanta Braves did when they signed Greg Maddux, then 27, in 1992, or the Boston Red Sox did when they traded for Martinez when he was 26, the Mets have acquired something irreplaceable: a pitcher established as the very best in the game with years left in his prime. It would be unfair to expect Santana to elevate his game, as Maddux and Martinez did by winning world championships and multiple Cy Young awards with their new teams. It would also be impossibly cynical not to wonder if he just might be able to do that.

Describing Santana as a two-time Cy Young award winner seems actually to diminish his achievements. He’s in his own class. Over the last four years, Santana struck out 983 batters; Jake Peavy is second, with 844, and no one else has struck out even 800. His earned run average over that time was 2.89; one other American League pitcher with at least 600 innings has below 3.60. Impossibly efficient, he’s never thrown 120 pitches in a game, and yet has pitched 25 more innings than anyone else in baseball over the last four years. He was dominant in his most recent playoff starts; he even won a Gold Glove award this year. And he did all this in perhaps the toughest division in baseball.

Past all this, Santana is, stylistically, a very good fit with the Mets. Despite his gaudy strikeout numbers and lively fastball, he’s a junkballer at heart, a changeup pitcher with terrific control, and so he gets a lot of flyball outs. Both Shea Stadium and Citi Field, due to open next year, have large outfields, and with Beltran in center, Ryan Church in right, and Endy Chavez on the bench, the Mets should have their usual fine outfield defense. Santana will be pitching in one of the more forgiving environments in baseball, and he’ll take advantage of it.

While Santana is in some sense a replacement for Tom Glavine, and in a much more significant sense one for the aging Martinez, it’s probably best to think of him as replacing Mike Pelfrey, until yesterday the nominal fifth starter. This is a lot of why this is not just a transcendently good trade, but a savvy deal dollar-wise.

The difference between Santana and what the Mets could expect from Pelfrey and a revolving door of no. 6 starters is worth something like six to eight wins, depending on your terms. According to sabermetrician Tom Tango’s research, the going rate for a projected win above what a no. 6-type would likely do is $4.4 million. This suggests not only that Santana is well worth $25 million a year, but that the Mets will be getting the full advantage of the expense. He’ll be worth less in future years, but so will $25 million, as baseball salaries inflate about 10% every year. And the wins here in question make the difference between the Mets being a strong contender and a strong favorite, greatly increasing the team’s chances of saying goodbye to Shea in style and of ringing up even more cash when Citi Field opens.

Whatever absurd price the Mets and Santana settle on, the Mets will pay it happily and no one will pay it any mind for a long time.

At a stroke, then, the Mets have regained their promise as the team of tomorrow, addressed their greatest weakness, and showed up the Yankees, all at a reasonable price; there must be a catch, no? Of course there must be, and here it’s the phrase “four prospects.”

Surely had you told Minaya, or any Mets fan, at the outset of these negotiations that he would only have to give up outfielder Carlos Gomez and pitchers Phil Humber, Delois Guerra, and Kevin Mulvey, he would have performed incredible athletic feats and kissed you. Gomez, while greatly talented, has more chance of being a fourth outfielder than he does of being an All-Star. Humber and Mulvey are right-handers without great stuff, likely back-end starters at best. And while Guerra pitched in High-A ball at 17 last year, he has long odds of ever making the majors at all, like any pitcher so young.

The Twins have specific ideas about what sorts of players they like, and there is a real chance all these players will thrive. Even if they perform up to their talent, though, the Mets really won’t miss them in end. Rich teams can always find a good outfielder or a passable back-end starter. Guerra might really haunt the Mets, but you have to give up something for Santana; far better to give up three pitching prospects rather than one real hitting prodigy such as Fernando Martinez, the Mets’ one true blue-chip prospect.

Still, while Minaya obviously had to give these players up, this trade does gut the team’s farm system and handcuff Minaya, at least for a while. Baseball America ranked Guerra as the Mets’ no. 2 prospect, Gomez no. 3, and Mulvey no. 4, with Humber no. 7; prospect analyst John Sickels had them in the same spot. Short of Martinez, the Mets really have nothing significant in their system now, and little way to improve should injury strike a team with plenty of old players and a thin bench.

If this is the worst concern that can be raised, though, Minaya has indeed done brilliantly, more than well enough to redeem an uninspiring winter. In every possible way, Santana is exactly what the Mets needed, and he’s exactly what the Mets got; their fans haven’t had a moment so good since Endy Chavez turned Scott Rolen’s home run into a double play in the last game of the 2006 playoffs. Now, they may even get to see what they should have seen a week after that catch — a World Series trophy held high in New York.

tmarchman@nysun.com