A good bullpen may not be sufficient to win a pennant, but it is necessary. Two years ago, Mets relievers rated first in the National League in earned run average, and the team came within outs of the World Series. Last year, they rated eighth and the team collapsed down the stretch in a blur of games decided by walks drawn from timid pitchers and home runs hit off tired ones. These were not coincidences.

Over the winter, the team’s main response to last year’s failures was to trade for Johan Santana. There’s something to the theory that one way to improve the bullpen is to improve the rotation. Replacing the crud at the back of the rotation with the game’s best and most durable pitcher will allow the team to rest the better relievers a bit more and use the worse ones a bit less, and that should lead to some tangible gains.

Still, the best way to fix a sketchy bullpen is to get better pitchers, and there the Mets have done nothing inspiring. They acquired Steven Register from Colorado in the Rule 5 draft, claimed Oakland’s Ruddy Lugo from the waiver wire, and signed fringe veteran Matt Wise to a $1.2 million contract, and there’s a reason why you have likely never heard of any of them. Duaner Sanchez is in camp, but hasn’t pitched since he broke his shoulder in a car crash two years ago. It’s the sort of injury that usually ends a career.

Most likely, the Mets’ bullpen will look much as it did last year. Billy Wagner will close, and Aaron Heilman will be the primary setup man. Each is among the better pitchers in the league in his role, though prone to occasional brief fits of temporary uselessness. Past them, everything looks, again, like a bit of a mess.

One culprit is an overabundance of situational pitchers. Scott Schoeneweis is used as one because he can’t get right-handed hitters out, Joe Smith is used as one because he can’t get left-handed hitters out, and Jorge Sosa should be used as one because he turns the average lefty into Todd Helton. Even Heilman, whose changeup has usually neutralized the left-handed threat, showed a worryingly large platoon split last year. None of this is made better by the use of Pedro Feliciano, who can get all hitters out but has had more games pitched than innings the last three years, a sign of how heavily he’s used in a specialist role.

More broadly, though, the problem is a lack of variety. Not only don’t the Mets have a single reliever who throws a good curveball, only Lugo really throws one at all. Heilman and Wagner are both hard throwers, but everyone else on the staff sits in the 88-to-93 range, the dead zone for relievers who get by with sliders, sinking action, and control. There’s nothing especially wrong with this kind of pitcher, but there’s nothing especially right about them, either. A reliever can dominate as long as he’s great at just one thing, but pitchers of this class never are.

This kind of bullpen can work, and the Mets’ probably will. It’s built for a game in which the starter puts in six or seven innings. When that happens, and it will happen more often than not, manager Willie Randolph will be able to go to the specialists to get good matchups, then give the ball to Heilman and Wagner. Wise and Feliciano should be able to set up if Heilman needs a rest, and the surfeit of tactically-oriented pitchers will allow all of them to be well-rested, too. There’s nothing much wrong with this arrangement.

If that’s the best that can be said of it, though, Mets fans will be right to be worried all through the year. The problem here is less the quality of the pitchers than the structure of the bullpen, which isn’t built to stand up to much stress. If the Mets get three awful starts in a row, it’s going to be badly strained. If Heilman continues to have problems with left-handers, there’s no obvious second plan. If the team has an important series coming up against a team that feasts on sinker/slider types, they won’t be able to do much about it.

These sorts of conditionals could be proposed to make any bullpen look bad, but the Mets are a clear favorite for the World Series, and they should be held to a high standard. A bullpen that offers some depth and variety is not too much to expect. This is a strong team in all aspects of the game, in a pitifully weak league, so Matt Wise and Pedro Feliciano are good enough to get the Mets to October. They aren’t enough to get them through it.

tmarchman@nysun.com