STOCKHOLM - Carmaker Saab said on Monday it was likely to unveil its new owner this week, and that three quarters of its creditors had agreed to a proposed writedown of the loss-making General Motors brand's debt.

A source told Reuters last week luxury carmaker Koenigsegg and Norwegian investors had reached a preliminary agreement to buy Saab Automobile, which was put up for sale by its now bankrupt U.S. parent earlier this year.

A Saab spokeswoman said an announcement should come soon.

I think that during this week, chances are good. It could be anytime now, spokeswoman Gunilla Gustavs said.

Saab, which first sought protection from creditors in February and was granted an extension until August 20 to get time to restructure and line up a new owner, said more than 80 percent of its creditors had agreed to write down the value of their Saab debt.

The Swedish carmaker has said it needs $1 billion in financing to see it through the crisis and has asked creditors to write off 75 percent of the company's 10.6 billion crown ($1.4 billion) debt, most of which is owed to GM.

Saab needs support from 75 percent of creditors, as well as from creditors holding 75 percent of its debt, for the writedown to be carried out, a process that is to be approved by a Swedish district court on Wednesday.

We are well above that, which is good. That makes Wednesday more or less a formality, Gustavs said.

The Swedish government said last week it had authorized the debt office to begin talks with the General Motors unit on state loan guarantees.

(Reporting by Veronica Ek; editing by John Stonestreet)