The Treasury Department said yesterday that it will need to raise about $11 billion during the third quarter of this year and said it will borrow $3 billion of that through sales of notes and bonds next week.

Roger C. Altman, assistant secretary of the Treasury for domestic finance, said the government already has borrowed or announced borrowings totaling $2.3 billion since July 1, so after next week it will have to raise about $5.7 billion by Sept. 30.

He said the government started the quarter with $16.9 billion in the till and wants to have about $12 in the Treasury on Sept. 30, which is the end of federal spending (or fiscal) year 1977.

Next week the Treasury will sell three issues that will pay back about $3.3 billion of maturing securities and raise net new cash of about $3 billion. They are:

$3 billion in three year notes, with a minimum purchase of $5,000 on Tuesday, Aug. 2.

$2.25 billion in seven-year notes, with a minimum purchase of $1,000 on Wednesday, August 3.

$1 billion of 29-year, six-month bonds with a minimum purchase of $1,000 on Thursday, aug. 4.

Altman said all of the new money the Treasury will raise this quarter probably will be done through coupon securities (notes and bonds) rather than through bills. Bills are short-term securities (maturing in less than a year) and are auctioned in regular weekly and monthly sales.

Unlike notes and bonds, which carry a coupon paying interest on the face amount, bills are sold at a discount (less than face value) and the total interest a investor receivers is the difference between the purchase price and the face value when the security is redeemed.

The Treasury temporarily was flush with cash during the quarter ended June 30 and paid off about $4 billion of the national debt.