WASHINGTON (AP) — Interest rates on short-term Treasury bills fell in Monday's auction to their lowest levels in four weeks.

The Treasury Department auctioned $48 billion in three-month bills at a discount rate of 1.715 percent, down from 1.740 percent last week. Another $42 billion in six-month bills was auctioned at a discount rate of 1.880 percent, down from 1.905 percent last week.

The three-month rate was the lowest since those bills averaged 1.670 percent on March 12. The six-month rate was the lowest since those bills averaged 1.850 percent, also on March 12.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,956.65 while a six-month bill sold for $9,904.96. That would equal an annualized rate of 1.746 percent for the three-month bills and 1.924 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, stood at 2.06 percent on Friday, down slightly from 2.08 percent at the beginning of last week on April 2.