It’s time for Washington Redskins General Manager Bruce Allen to step up. He has to become more engaged in the fight. Clearly, the Redskins need more of a two-headed approach to team-building, because their solo act has flopped.

Whether or not Coach Mike Shanahan requests additional help on future major player-personnel matters, Allen must insist on providing his, because Shanahan clearly needs it.

The guy who chooses Washington’s players is undermining the guy who leads them on the field. The Redskins’ problem is the same guy is doing both jobs: Shanahan.

In most organizations, that’s not the case. Many owners believe those key responsibilities are too much for one person. They would rather not have two big hats atop one head.

Coaches are trained to work with the rosters their general managers provide. They’re expected to help players overcome weaknesses and sharpen their strengths by putting them in positions to excel. Some coaches expect to succeed with even marginal players, figuring they just need to “coach ’em up.”

General managers, at least the good ones, view things differently. For them, it’s about critically analyzing players and making honest assessments about whether coaching, even great coaching, would make a significant difference in their performances.

During Shanahan’s first two seasons leading Washington, he has made three horrendous choices selecting Redskins quarterbacks — and that’s at least two too many. Shanahan’s blunders derailed the team on the field, stirred frustration within the locker room and set back the franchise, which owner Daniel M. Snyder had hoped would improve steadily under the two-time Super Bowl winner.

The Redskins cannot afford another big error at the game’s most important position. In Shanahan’s third offseason in charge, they have to get it right.

After a 3-1 start, Washington has lost five straight games. Its offense ranks among the NFL’s worst. Although injuries have contributed to the group’s ineptitude, ineffective quarterback play is Washington’s main problem.

Shanahan, who has ultimate player-personnel authority, believed that either the turnover-prone Rex Grossman or the inexperienced John Beck could successfully direct the offense.

Each has been benched in the first nine games. Neither provides a short- or long-term solution to Washington’s unstable quarterback situation.

Before the preseason, some Redskins people privately raised concerns about Shanahan’s quarterback choices, believing neither Grossman nor Beck was the answer. Then Shanahan said he would stake his reputation on both being effective.

Shanahan’s Rex-Beck backing came after the spectacular failure of Donovan McNabb, who started for the first 13 games last season. Shanahan traded for McNabb because he apparently saw him as an upgrade over Jason Campbell, whom he shipped to the Raiders weeks later. Campbell is a friend of mine, but you don’t have to be his friend to acknowledge he’s better than Beck.

So that’s four poor decisions at quarterback made by Shanahan in two years. Allen should try to prevent a fifth. The Redskins need him to offer another strong voice on the biggest decisions involving players. And if Allen already has tried, he needs to speak even louder now.

Shanahan’s belief in Grossman and Beck was really about his belief in himself as a coach. Shanahan figured his coaching could elevate their play.

Washington’s player-personnel boss hurt Washington’s coach. As a result, the Redskins were finished before the season even started.

The Redskins, who have many questions on offense, must develop a better system of checks and balances. They can’t begin another season ill-equipped at quarterback because of Shanahan’s confidence in his coaching ability. Washington needs Allen to stand up to Shanahan. In the Redskins’ organization, there’s no one else to do it.

Allen may need Snyder’s help in persuading Shanahan to try something new. Fortunately for Allen, he has Snyder’s ear, Redskins people say.

Allen is savvy. He’s a shrewd, tough executive. He knows all the angles and is always focused on the big picture.

Because of his family ties to the franchise, Allen was eager to take part in attempting to restore the Redskins. He understood Shanahan would have the upper hand in the Redskins’ non-traditional GM-coach dynamic.

Still, Allen has played a key role in the football operation, especially from a budget planning perspective. Allen also is active in the Redskins’ community efforts. He has worked hard to improve ties with the team’s alumni.

Allen’s accomplishments, though, won’t matter much unless the Redskins get back to winning. He knows that. He’s too smart to think otherwise.

Player-personnel isn’t Allen’s area, NFL people say. Many of the moves Allen made while running the Tampa Bay Buccaneers were roundly criticized.

The Redskins, however, don’t need Allen to project whether an 18-year-old college guard will become another Russ Grimm. He doesn’t have to be a guru.

He just has to push back when Shanahan is charging too hard. He has to call for substantive discussion before Shanahan declares only one voice is necessary. Allen must prevent another Rex-Beck fiasco from happening again.

The Redskins are in good shape with their salary cap, mostly because of Allen and Eric Schaffer, the club’s talented vice president of football administration. Morocco Brown, director of pro personnel, is one of the league’s top young talent evaluators. He could run his own shop someday.

Based, in part, on front-office recommendations, Shanahan selected impressive outside linebacker Ryan Kerrigan with the first pick in the April draft. During free agency, Shanahan approved the signings of defensive end Stephen Bowen and nose tackle Barry Cofield, who have bolstered Washington’s 3-4 attack.

Shanahan has made some good moves. He’ll soon have another opportunity to pick a quarterback. Allen should make sure he doesn’t do it alone.