WASHINGTON — Interest rates on short-term Treasury bills rose in Monday’s auction to their highest levels since the fall of 2008.

The Treasury Department auctioned $42 billion in three-month bills at a discount rate of 1.285 percent, up from 1.240 percent last week. Another $36 billion in six-month bills was auctioned at a discount rate of 1.415 percent, up from 1.360 percent last week.

The three-month rate was the highest since those bills averaged 1.420 percent on Sept. 22, 2008. The six-month rate was the highest since those bills averaged 1.800 percent on Oct. 20, 2008.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,967.88 while a six-month bill sold for $9,928.86. That would equal an annualized rate of 1.307 percent for the three-month bills and 1.445 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, rose to 1.60 percent Friday, up from 1.55 percent at the beginning of last week on Nov. 13.