Yields on three-month Treasury bills fell at yesterday's auctions for the ninth consecutive week, dropping rates to their lowest levels in a year. The yield on the six-month bill also declined, after having increased last week.

The government sold $6.8 billion in three-month bills at an average discount rate of 8.82 percent, down from 9.38 percent last week. Rates have been declining since reaching a high of 10.63 percent on Sept. 4. The government sold $6.8 billion in six-month bills at an average discount rate of 9.07 percent, down from 9.59 percent last week. Before last week's increase, six-month bills also had declined every week since Sept. 4.

The yield on the three-month bill was the lowest since Nov. 21, 1983, when it was 8.81 percent, while the 9.07 percent rate on six-month bills was the lowest since Jan. 30, when it was 8.97 percent.

The new discount rates understate the actual returns of 9.14 percent for three-month bills and 9.64 percent for six-month bills.

Meanwhile, the Treasury sold $6.5 billion of three-year notes at an average yield of 11.01 percent, down from 12.46 percent at the last such auction on Aug. 15. The average dollar price was 99.975; the coupon rate, 11 percent.