WASHINGTON — College students taking out new loans for the fall term will see interest rates twice what they were in the spring — unless Congress fulfills its pledge to restore lower rates when it returns after the July 4 holiday.

Subsidized Stafford loans, which account for roughly a quarter of all direct federal borrowing, went from 3.4 percent interest to 6.8 percent interest on Monday. Congress’ Joint Economic Committee estimated the cost passed to students would be about $2,600.

Efforts to keep interest rates from doubling on new Stafford loans fell apart last week amid partisan wrangling in the Senate. Democratic senators and the White House both predicted that a deal would be reached in Congress to bring the rates down again before students return to campus.

But if an agreement remains elusive, students could find themselves saddled with higher interest rates this year than last.

“The only silver lining is that relatively few borrowers take out student loans in July and early August. You really can’t take out student loans more than 10 days before the term starts,” said Terry Hartle, a top official with colleges’ lobbying operation at the American Council on Education.

Students only borrow money for one school year at a time. Subsidized Stafford loans taken before Monday are not affected by the rate hike, nor are federal PLUS, Perkins or unsubsidized Stafford loans slated for the coming year.