WASHINGTON | Interest rates on short-term Treasury bills rose in Monday's auction with six-month rates climbing to the highest level since early September.

The Treasury Department auctioned $25 billion in three-month bills at a discount rate of 1.250 percent, up from 0.500 percent last week. Another $26 billion in six-month bills was auctioned at a discount rate of 1.800 percent, up from 1.100 percent last week.

The three-month rate was the highest since these bills averaged 1.420 percent on Sept. 22. The six-month rate was the highest since these bills averaged 1.900 percent Sept. 8.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,968.40 while a six-month bill sold for $9,909.00. That would equal an annualized rate of 1.271 percent for the three-month bills and 1.842 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 up to 1.25 percent last week from 1.24 percent the previous week.