WASHINGTON (AP) — Interest rates on short-term Treasury bills rose in Monday's auction to the highest levels this year. The Treasury Department auctioned $24 billion in three-month bills at a discount rate of 0.050 percent, up from 0.030 percent last week. Another $24 billion in six-month bills was auctioned at a discount rate of 0.145 percent, up from 0.135 percent last week. The three-month rate was the highest since three-month bills averaged 0.055 percent on Dec.