BOSTON — It seemed like a logical enough gamble at the time.

Bereft of power in the upper levels of their minor league system and believing they had a surplus of starters, the Red Sox, some 14 months ago, traded depth for need, sending Bronson Arroyo to Cincinnati for Wily Mo Pena.

When the Sox proceeded to lose Matt Clement, Tim Wakefield and David Wells for significant stretches of the ill-fated 2006 season, the deal backfired in a big way. By mid-season, the Red Sox were turning to such luminaries as Jason Johnson and Kevin Jarvis to start games for them.

In the meantime, Arroyo merely led the National League in innings pitched while winning 14 games for the Reds.

Even now, the Red Sox could use Arroyo. But the more pertinent question might be: do they still have any use for Pena?

It’s a question worth asking again after last night. The Sox had Pena in the lineup, theorizing that it would be a good opportunity to get him some at-bats against a young lefty (Brian Burres) while at the same time providing a night off for the slumping J.D. Drew.

As it turned out, Pena went 0-for-3, but that wasn’t nearly an issue. For the second time in the last three home series, Pena grossly mishandled a routine fly ball for a costly error.

Last night’s miscue came in the three-run Baltimore fifth. With Melvin Mora on second and two outs, Jay Gibbons hit a liner more or less directly at Pena. But as Pena charged in to make the catch, the ball hit the heel of his glove and got away. Mora scored.

Pena said he never picked the ball out of the lights and “tried to get around it. But it was in the lights. There was nothing I could do.”

Just one batter earlier, Pena had got himself twisted while drifting back on a Melvin Mora shot that one-hopped the bullpen for a ground rule double. It would have been a remarkable catch, but it again seemed to highlight Pena’s poor instincts in the field.

Only three weeks ago against Toronto, Pena, filling in for Coco Crisp in center, made a similar gaffe, contributing to a Red Sox’ loss to Toronto.

No one is expecting Pena to provide Gold Glove-caliber defense in the outfield. But when he fails to make routine plays, he becomes a liability.

The Red Sox don’t ask him to serve as a late-inning defensive replacement in close games. But when Pena makes embarrassing errors like the one he committed last night, he becomes dead weight on the Boston bench.

It’s not as if his offense makes up for his shortcomings in the field. After last night, Pena is hitting .232 with two homers and five RBI in 22 games. In 43 at-bats, he has just four extra-base hits. Nearly half of his at-bats (19) have resulted in strikeouts, continuing a career-long trend.

Occasionally, Pena can tease you with his awesome power. His grand slam on April 26, crushed into the back bullpen at Camden Yards, was a thing of beauty and gave the Red Sox a come-from-behind 5-2 win. Similarly prodigious homers — a tape-measure shot in Kansas City last August comes immediately to mind — tend to make impressions.

But these bursts of power are too infrequent. Unfortunately, the same can’t be said for his maddening habit of chasing breaking balls out of the strike zone, which he does with alarming frequency.

It’s hard to envision Pena breaking out of this cycle. He needs regular playing time to find consistency at the plate, but the Sox can’t afford to play him regularly until he shows consistency. And around and around it goes.

One American League official this week said that Pena still has some trade value, though it seems to be decreasing almost daily. No doubt, some team would take a chance on his potential, just as the Yankees, Reds and Red Sox once did.

“It’s just a matter,” said the official, “of how little they would take.”

Small-market teams in search of some pop might be tempted since Pena is still young (25) and relatively affordable ($3 million) and under control through next season. Out of the spotlight and given the opportunity to play every day, he could still develop.

But with each passing day, Pena’s role here is less clear. He’s not a particularly adept pinch-hitter, and anyway, the Sox usually only hit for their second baseman. If the Sox need a righthanded-hitting outfielder to spell Drew on occasion, surely one can be found.

In the meantime, it would seem time to move on. What seemed like a logical gamble at the time is, more and more, resembling a big mistake.