WASHINGTON » Troubled mall owner General Growth Properties Inc., trying to stave off a bankruptcy filing, said it is still trying to negotiate an extension on $900 million in debt that was due to be repaid yesterday, but warned there can be “;no assurance”; it will get a reprieve.

Investors, however, appeared optimistic that a bankruptcy filing would be avoided. Shares rose 36 cents, or 25 percent, to close at $1.80 in the regular session. The stock rose another 7 cents after hours.

The mortgages cover two Las Vegas malls, Fashion Show and Palazzo. Earlier this month, Chicago-based General Growth received a two-week extension on the loans. The company's holdings also include Ala Moana Center and Ward Centers. General Growth put Ward Centers up for sale earlier this month.

General Growth also said yesterday it refinanced a separate $896 million worth of loans, retiring a $58 million bond that matured Thursday and $814 million of debt scheduled to mature next year.

The nation's second-largest shopping mall owner has been hit hard by the credit crunch, as it piled up a staggering debt load during the real estate market's boom years. Analysts are unsure whether new managers, installed in late October, will be able to keep the company afloat as the recession drags on and U.S. retailers struggle. The company last month hired law firm Sidley Austin as an adviser.

General Growth has a stake in more than 200 shopping malls in 44 states. It is trying to sell its Las Vegas locations.

If General Growth files for bankruptcy protection, Fitch Ratings said yesterday it doesn't expect to lower ratings on commercial mortgage-backed securities that are exposed to General Growth's assets. Defaults on corporate loans will not trigger a default on its mortgage-backed securities, Fitch said, because they are legally separate entitles and are isolated from their corporate parent.