NEW YORK, May 4 (Reuters) - The U.S. Treasury said on Monday it expects to borrow $189 billion in the second quarter, $79 billion higher than the February estimate primarily due to lower than projected net cash flows that were partially offset by higher than expected cash balance at the beginning of the quarter.

The second-quarter financing estimate assumes a cash balance of $900 billion at the end of June, the Treasury said in a statement.

The Treasury also said it expects to borrow $671 billion in the third quarter, as it forecasts a cash balance of $950 billion at the end of September.