The clock has all but run out on the defense industry’s efforts to stave off billions in looming budget cuts under sequestration.

At the Pentagon, administration officials have given Defense Department number crunchers the green light to begin planning for the $500 billion in budget cuts set to go into effect in January.

Weeks of intense, last-minute negotiations between Speaker John Boehner (R-Ohio) and President Barack Obama on a potential deal to avoid January’s “fiscal cliff” of looming tax hikes and automatic spending cuts appeared to come to an unceremonious end last Thursday.

After a furious effort to draw GOP support for his “Plan B” tax proposal, the Ohio Republican was forced to pull his bill from the floor, unable to secure the 218 votes needed for passage.

Boehner’s defeat at the hands of his own party draws the curtain on a multimillion-dollar campaign by top defense industry lobbyists and interest groups to gin up opposition to the sequestration plan.