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 in Honolulu.

General Growth also said 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.

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

General Growth stock is down 95 percent over the past six months.

Last month, the company reported disappointing third-quarter results and cut its year-end forecast, weeks after the mall owner's board removed its chief executive, president and chief financial officer.

Their ouster came after the company disclosed that former CEO John Bucksbaum's family trust provided $90 million in personal loans to cover margin debt for the former chief financial officer and president.

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.

The credit ratings agency, however, warned that under a bankruptcy filing, the amount of money available for property maintenance and renovation could be limited, leading to deteriorating financial performance of the properties.