The country’s biggest business lobby sat on the sidelines on the great debt debate for weeks, prodding Congress to strike a deal to avoid defaulting on the country’s debt. But on Tuesday it finally picked sides, urging lawmakers to rally behind a temporary solution offered by House Speaker John Boehner.

The decision by the Chamber of Commerce could tilt the balance as lawmakers weigh competing plans from Boehner and Senate Majority Leader Harry Reid. Showing its muscle, the chamber delivered a letter to all 535 lawmakers’ offices on Capitol Hill. It also has local chapters in nearly every major community in the country that can be activated if needed to press for a deal, as America stumbles dangerously close to an Aug. 2 deadline for defaulting.

“While no legislation is perfect, [Boehner’s plan] is a responsible approach,” wrote Bruce Josten, the chamber’s top lobbyist. Its key virtues, he says, are that it raises the debt ceiling, paves the way for more spending cuts, and sets up the possibility of a balanced-budget amendment.

The chamber’s tepid endorsement reflects its anxiousness. At this point the business community wants a deal, almost any deal, rather than default. And Boehner’s was the furthest along.

“Our priority is ensuring the debt ceiling is increased,” the chamber’s Blair Latoff told The Daily Beast. “At this time, there isn’t another viable piece of legislation out there. Supporting Speaker Boehner’s proposal does not preclude us from supporting others.”

Boehner’s plan would require Congress to address the debt ceiling at the end of this year, just as the 2012 presidential-election campaign begins. Reid’s plan forestalls another debate until 2013. Otherwise, the two plans are similar in many respects, including not proposing any tax increases.

The chamber’s choice puts it on the opposite side of others in the business community. The influential National Taxpayers Union, the Club for Growth, and the policy wing of the Heritage Foundation have opposed Boehner’s plan, showing a deep rift among business leaders fearful of default.

President Obama supports Reid’s plan, and the White House declined to comment Tuesday on the chamber’s letter. But the Office of Management and Budget earlier in the day issued a veiled veto threat for Boehner’s bill, saying advisers would recommend a veto. Obama hasn’t yet addressed the legislation personally.