WASHINGTON — Interest rates on short-term Treasury bills fell in Monday’s auction with rates on three-month bills dropping to the lowest point since January.

The Treasury Department auctioned $30 billion in three-month bills at a discount rate of 0.075 percent, down from 0.085 percent last week. Another $27 billion in six-month bills was auctioned at a discount rate of 0.130 percent, down from 0.140 percent last week.

The three-month rate was the lowest since three-month bills averaged 0.050 percent on Jan. 30. The six-month rate was the lowest since these bills averaged 0.125 percent on Feb. 21.

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 0.19 percent last week from 0.21 percent the previous week.