WASHINGTON — Interest rates on short-term Treasury bills fell in Monday's auction, with three-month bills dropping to their lowest levels since late November.

The Treasury Department auctioned $24 billion in three-month bills at a discount rate of 0.025 percent, down from 0.030 percent last week. Another $24 billion in six-month bills was auctioned at a discount rate of 0.085 percent, down from 0.110 percent last week.

The three-month rate was the lowest since those bills averaged 0.020 percent on Nov. 24. The six-month rate was the lowest since those bills averaged 0.075 percent on Dec. 1.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,999.37, while a six-month bill sold for $9,995.70. That would equal an annualized rate of 0.025 percent for the three-month bills and 0.086 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 0.24 percent last week from 0.25 percent the previous week.