The United States could begin defaulting on its obligations between the end of October and the middle of November if Congress fails to increase the $16.7 trillion federal debt limit, Congressional Budget Office director Doug Elmendorf said on Tuesday.

Elmendorf told a news conference that the U.S. Treasury Department's own estimate that it will run out of borrowing capacity in mid-October, with a $50 billion cash balance, "seems plausible to us" based current Treasury cash flows. It will start to run short of cash to pay obligations starting around the end of October, but the timing for this could shift based on the strength of revenue collections, he said.

(Reporting by David Lawder; Editing by Vicki Allen)