Interest rates on short-term Treasury bills fell in Monday's auction.

The Treasury Department auctioned $24 billion in three-month bills at a discount rate of 1.865 percent, down from 1.900 percent last week. Another $23 billion in six-month bills was auctioned at a discount rate of 2.060 percent, down from 2.135 percent last week.

The three-month rate was the lowest since June 23, when these bills averaged 1.855 percent. The six-month rate was the lowest since these bills averaged 2.050 percent on June 9.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,952.86 while a six-month bill sold for $9,895.86. That would equal an annualized rate of 1.900 percent for the three-month bills and 2.111 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, fell to 2.35 percent last week, from 2.46 percent the previous week.