WASHINGTON | Interest rates on short-term Treasury bills fell in Monday's auction to the lowest levels since June.

The Treasury Department auctioned $21 billion in three-month bills at a discount rate of 4.770 percent, down from 4.825 percent last week. Another $18 billion in six-month bills was auctioned at a discount rate of 4.730 percent, down from 4.800 percent last week.

The three-month rate was the lowest since three-month bills averaged 4.685 percent on June 25. The six-month rate was the lowest since 4.715 percent on June 18.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,879.43 while a six-month bill sold for $9,760.87.

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 4.83 percent last week, down from 4.91 percent the previous week.