Interest costs to the government, as measured by weekly Treasury auctions of 13-week and 26-week bills, rose yesterday for the second consecutive week.

The average discount rate on 13-week bills was 11.101 percent compared with 10.404 percent last week, and it was the highest since 11.128 percent on Nov. 9. The investment rate, or equivalent coupon-issue yield, was 11.58 percent compared with 10.83 percent for the previous bill auction a week ago.

For 26-week bills, the discount rate was up to 11.595 percent from 10.772 percent, and it was the highest since 12.721 percent on Nov. 2. Equivalent coupon-issue yields rose to 12.49 percent from 11.55 percent a week ago. The Treasury sold $4.7 billion each of the 13-week and 26-week bills.

Top interest rates on six-month money market certificates at banks and savings and loan associations will go up because of yesterday's auction to 11.845 percent starting this morning from 11.09 percent. The rate is determined by adding a quarter percentage point to the average yield on 26-week bills or to the average of the four most recent weeks, whichever is higher. Credit unions follow four different formulas to set ceilings, and individual institutions should be contacted for current rates.