The federal government has rejected the state’s request for disaster aid for the deadly natural gas pipeline explosion in San Bruno.

The decision, an appeal of which is likely, means the state will not receive millions of dollars in disaster relief money to cover the costs of the calamity

The Federal Emergency Management Agency determined the damage was “not of such severity and magnitude” as to overwhelm the state and local agencies that responded to the Sept. 9 blast, according to the letter that Gov. Arnold Schwarzenegger received from the agency Friday. The letter goes on to say that help from other sources, including PG&E, will be enough to meet the needs of the event.

However, FEMA will reimburse the state for up to 75 percent of the firefighting costs, agency spokesman Bradley Carroll wrote.

But San Bruno Mayor Jim Ruane, who testified before a Senate committee on pipeline safety Tuesday, said Schwarzenegger plans to appeal the decision. Ruane said he was surprised and disagreed with FEMA’s conclusion that the city will be able to pay for the response and cleanup.

“How are you going to know now what this is going to cost?” he asked, adding that the damage estimate alone is more than $50 million, and that doesn’t include millions of dollars to cover the cost of the police and firefighters who battled the blaze.

“This is not going to be a cheap undertaking,” Ruane added.

The state has 30 days to appeal the decision and must provide additional information to show why the money is needed, said Kelly Huston, spokesman for the California Emergency Management Agency.

He said an appeal would include the latest damage figures, including the cost of removing hazardous waste from the site. If any money does eventually come from FEMA, it would go to help homeowners as well as the city with rebuilding infrastructure.

Huston said the money FEMA has already pledged might go toward paying more than firefighting costs. He said the agency could decide to help San Bruno cover the cost of having police guard the site as well as emergency shelters and other efforts.

Carroll said federal help is given when the costs of a disaster are too much for state and local governments. Part of making that determination is looking at whether there were “large numbers of injuries and deaths,” if there was a high concentration of damage or whether it was widespread, Carroll wrote.

Federal officials also consider whether insurance will pay for the recovery. Federal law prohibits the agency from covering costs that insurance should reimburse.

During the hearing Tuesday, U.S. Sen. Barbara Boxer, D-Calif., pledged to help with the appeal of FEMA’s decision.

Contact Joshua Melvin at 650-348-4335.