WASHINGTON — Interest rates on short-term Treasury bills fell in Monday’s auction to the lowest levels in two weeks.

The Treasury Department auctioned $39 billion in three-month bills at a discount rate of 1.040 percent, down from 1.045 percent last week. Another $33 billion in six-month bills was auctioned at a discount rate of 1.125 percent, down from 1.130 percent last week.

The three-month rate was the lowest since these bills averaged 1.000 percent two weeks ago on June 26. The six-month rate was the lowest since these bills averaged 1.110 percent, also on June 26.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,973.71 while a six-month bill sold for $9,943.13. That would equal an annualized rate of 1.057 percent for the three-month bills and 1.147 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, stood at 1.22 percent on Friday, down from 1.24 percent at the start of last week on July 3.