WASHINGTON (AP) — 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.

The three-month rate was the lowest since three-month bills averaged 0.040 percent on Dec. 17. The six-month rate was the lowest since 0.090 percent, also on Dec. 17.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,998.36 while a six-month bill sold for $9,994,69. That would equal an annualized rate of 0.066 percent for the three-month bills and 0.107 percent for the six-month bills.

Separately the Federal Reserve said Monday that the average yield for one-year Treasury bills, a popular index for making changes in adjustable rate mortgages, edged down to 0.15 percent last week from 0.16 percent in the previous week.