Treasury bill average yields were down this week on 29 3/4-year bonds and 9 3/4-year notes auctioned yesterday and Wednesday.

The Treasury sold $2.25 billion of 29 3/4-year bonds at an average annual yield of 12.68 percent yesterday, down from the 12.81 percent average annual yield on 30-year securities auctioned lst Nov. 7 and the lowest since an average 10.71 percent on Aug. 7.

The department received $5.25 billion in tenders for the bonds and accepted those in a range of 12.63 percent to 12.70 percent, including $238 million of noncompetitive tenders at the average return.

On Wednesday, the Treasury sold $2.5 billion of 9 3/4-year notes at an average annual yield of 12.89 percent.

The return was down from the record 13.07 average annual yield on 10-year notes auctioned last Nov. 17 and was the lowerst since a 10.81 percent average on 10-year notes sold last Aug. 6.

The department received $4.48 billion in tenders for the notes and accepted those in a range of 12.83 percent to 12.94 percent, including $323 million of noncompetitive tenders at the average return.