With this pen, things may only get worse

As the only member of the Mets’ already-infamous class of free agents who is currently on the active roster, Anthony Swarzak was charged with the duty of salvaging some honor for the group as the curtain closed on this dreadful first half of the season.

A simple three outs in the seventh inning of a tie game against the walking-dead Nationals didn’t seem like too much to ask.

Alas, Swarzak couldn’t even get one out before Mickey Callaway decided he’d seen enough, having watched the reliever walk the only two batters he faced.

And even that quick hook couldn’t prevent the disaster that ensued, as the atrocious bullpen exploded one last stink bomb on the mound to send the Mets to the All-Star break with 55 losses, the most they’ve had in the first half since 1993 — a season that saw both the manager and GM fired.

This season has a similar doomsday feel to it, with the GM job already in flux after Sandy Alderson stepped aside for health reasons, and ownership preparing to inter- view outside the organization in the coming months.

As for Callaway, the Mets seem to be trying to calm the waters around him, putting the word out that he’ll likely be back next season, but at this point that means little, depending almost entirely on whether the rookie manager makes strides to avoid the embarrassing mistakes that marked his first half.

Not to mention that if Jeff and Fred Wilpon want to attract first-rate candidates for the GM position, they can’t have an ironclad decision on the manager about which the new guy would have no say.

The point is, there’s a long way to go before any major decisions are made, and for the moment everyone around the Mets is simply relieved the All-Star break gives them four days to get away from everything that has gone wrong.

Just when it seemed they were starting to play better baseball, in fact, they have the type of bullpen meltdown at Citi Field on Sunday that has been a problem all season, allowing the Nationals to score five runs in the seventh inning to turn a tie game into a 6-1 loss.

By the time the inning was over, there was plenty of blame to spread around among Swarzak, Tim Peterson and Jerry Blevins — and let’s be honest, Blevins has killed the Mets this season as a lefty specialist who can’t get lefties out, his ERA now at a sparkling 5.01.

Yet there was no getting around the symbolism of Swarzak’s role in finishing off this first half in all-too appropriate fashion.

In a free-agent class loaded with bullpen options, Swarzak was the one early signing the Mets made last offseason, as they were convinced that his breakthrough season at age 31 with the White Sox and Brewers made him worthy of a two-year, $14 million deal.

And suffice it to say they couldn’t have made a worse choice, based on Swarzak’s first half.

Bad enough that he missed nearly two months with an oblique injury, but since returning the righthander has been one of the least effective relievers in baseball, allowing an average of nearly two baserunners per inning while compiling a 7.47 ERA.

And so, as it turned out, the Mets would have been better off on this day if Swarzak were still on the disabled list with the rest of his free-agent classmates, Jay Bruce, Todd Frazier and Jason Vargas.

And let’s not forget Jose Reyes, whose presence on the roster and regular playing time, despite his woeful lack of production, becomes more baffling by the day.

Now the Mets seem determined to patch the holes in the roster and try to win next season rather than enduring even a semi-rebuild. And because they’ll get little help coming from the farm system, that means going back into the free-agent market to rebuild the bullpen and find some offense.

But if they’re going to go bargain-shopping again for free agents in their 30s, as they did last winter, that’s hardly the best way to build a winner.

In truth, however, these Mets were built more to win games in big ways, with power bats and strikeout pitchers.

Yet the blueprint has failed miserably so far, in part because of their free-agent signings. And so it was indeed fitting that Swarzak set one last ugly first-half loss in motion because he couldn’t even throw a strike.