WASHINGTON (AP) — Interest rates on short-term Treasury bills fell in Monday's auction to the lowest levels in a month.

The Treasury Department auctioned $30 billion in three-month bills at a discount rate of 0.090 percent, down from 0.10 percent last week. Another $27 billion in six-month bills was auctioned at a discount rate of 0.145 percent, down from 0.150 percent last week.

The three-month rate was the lowest since three-month bills averaged 0.085 percent four weeks ago on June 11. The six-month rate was the lowest since it averaged 0.140 percent, also on June. 11.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,997.73, while a six-month bill sold for $9,992.67. That would equal an annualized rate of 0.091 percent for the three-month bills and 0.147 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 0.20 percent last week from 0.21 percent the previous week.