UPDATE 3-Saab secures debt writedown, Koenigsegg upbeat

* Swedish court approves Saab debt writedown

* Majority of creditors back 75 percent writedown

* Decision a step towards Koenigsegg takeover

* CEO says new owner to stick with Saab business plan

* Koenigsegg sees positive cash flow after 2010 (Adds quotes, background, more details)

By Johan Ahlander

VANERSBORG, Sweden, June 17 (Reuters) - Saab Automobile secured a key court ruling on Wednesday to cut almost $1 billion in debt owed mainly to U.S. parent General Motors, moving a step closer to new ownership by luxury sportscar maker Koenigsegg.

The ruling came after General Motors GMGMQ.PK said on Tuesday it would sell Saab to Koenigsegg in a proposed deal seen as one of the most unlikely in automotive history -- Koenigsegg made 18 cars last year, Saab more than 93,000.

Christian von Koenigsegg, founder of the Swedish firm that rolls out cars that cost about $1 million each, told Reuters a final deal with GM could still be more than two months away.

Koenigsegg said a newly formed group which plans to buy Saab had strong backing and that the goal of generating positive cash flow at Saab after 2010 was "fairly reasonable" but hinged on economic conditions.

"Our ambition is to turn the company around and keep it for the long term," he said, responding to criticism that the firm may be too small to take over Saab. "We are entrepreneurs. We are not venture capitalists."

A court in Vanersborg, near Saab's headquarters in southwest Sweden, approved a 75 percent writedown of Saab's more than 10 billion Swedish crowns ($1.28 billion) of debt after a vast majority of creditors gave the green light to the proposal.

Saab filed for protection from creditors in February after General Motors, itself now bankrupt, said it would cut ties to the brand by the year-end.

The head of Saab told Reuters after the ruling he believed Koenigsegg had the financial muscle and technological prowess to turn the iconic Swedish brand around.

"This group has the financial strength and a long-term view which is key in the car industry," Saab Chief Executive Jan Ake Jonsson said, adding the new owner planned to stick to the Saab business plan.

"Smaller firms like Koenigsegg have a somewhat different take on how to drive development and production, and they have cutting-edge know-how that we can benefit from."