But Kim Belshe, secretary of the state Health and Human Services Agency, said the administration continues to support a newly effective state law that bans a mercury-based preservative known as thimerosal from vaccines given to pregnant women and children younger than 3.

"We take very seriously the expressed concerns that mercury in vaccines causes autism and remain committed to full implementation of AB 2943," Belshe said.

Belshe issued the waiver at the request of the California branch of the American Academy of Pediatrics, Kaiser Permanente, the California Medical Association and the California Academy of Family Physicians.

Because of delays in vaccine production, pediatricians have received only partial orders of the mercury-free influenza shots and thus have not been able to protect young children as the flu season approaches, the medical groups said.

Yet many doctors have flu shots available with thimerosal.

Gov. Arnold Schwarzenegger endorsed the temporary waiver and fired off a letter Thursday to Sanofi Pasteur, the lone manufacturer of mercury-free children's vaccine, encouraging the firm to beef up its production.

The actions won praise from pediatricians and some in the autism community who were pleased the waiver is temporary.

"This is excellent," said Dr. RandyBergen, chief of pediatrics at Kaiser Permanente in Walnut Creek. "Hopefully, Sanofi will be able to ship sufficient supply within six weeks so the children of California will be adequately protected."

The firm expects to fill all of its orders by the end of November, a spokeswoman said.

Kaiser is in better shape than many organizations because it has received 80 percent of the 105,000 thimerosal-free doses ordered for Northern California children, Bergen said.

Pediatricians say they must move quickly because young children need two flu shots, one month apart, the first time they are immunized for the disease. The flu season typically peaks anytime from late November through February.

Although her group opposed the waiver, Bobbie Manning said she was glad to hear top California officials support the state law.

"I hope there will not be another request for a waiver at the end of the six weeks," said Manning, a board member of Advocates for Children's Health Affected by Mercury Poisoning (A-CHAMP).

Rick Rollens, the father of an autistic child and co-founder of the MIND Institute at UC Davis, supported the waiver since it is temporary.

"It took a lot of courage for the governor to sign this bill to begin with," Rollens said. "He had a tough decision to make on this issue and I think he has taken the right step."

Others saw it differently. J.B. Handley, a former Lafayette resident and the father of an autistic son, said state officials should launch an informational campaign to ensure parents know the flu shot their child receives may contain thimerosal.

"The state of California has an obligation to inform parents of this backward step that is re-introducing a neurotoxin to young children," Handley said.

Dr. Myles Abbott, an Orinda pediatrician who signed the letter to the state on behalf of the American Academy of Pediatrics, sought to allay fears that his group would seek a permanent waiver.

"Hopefully, this will never have to occur again," he said.

"Although the science doesn't say (thimerosal) is dangerous per se, we don't feel you have to have extra components (in vaccines) and we'd like to get them out," he said. "We want to honor what the law is, but this is an exceptional year."