The Treasury's projections, released in Washington Monday, come as longer-term borrowing needs depend on the fate of two fiscal packages being finalized in Congress. U.S. debt managers expect to borrow $1.02 trillion in the October-December period, about $312 billion more than the $703 billion in net marketable debt issuance it anticipated in August.

The tallies are based on the assumption that lawmakers raise or suspend the federal debt limit. Congress last month boosted the ceiling by a limited amount, with the Treasury's borrowing authority set to run out as soon as next month.

The Treasury trimmed its cash balance estimate for the end of December to $650 billion, below the $800 billion it previously projected. Officials have been constrained in building a bigger buffer by the maneuvers they've had to take to stay within the debt limit.