WASHINGTON — Interest rates on short-term Treasury bills fell in Monday’s auction to the lowest levels in three weeks.

The Treasury Department auctioned $32 billion in three-month bills at a discount rate of 0.065 percent, down from 0.075 percent last week. Another $28 billion in six-month bills was auctioned at a discount rate of 0.105 percent, down from 0.120 percent last week.