In preparation for swine-flu vaccinations next month, Washington’s Health Department on Thursday temporarily suspended a rule that limits the amount of a mercury preservative in vaccines given to pregnant women and children under the age of 3.

The preservative, thimerosal, has never been linked to any health problems, said Secretary of Health Mary Selecky. But a vocal minority believes the compound could be linked to autism. The state Legislature adopted the limit in 2006.

Thimerosal has been eliminated from most vaccines in the United States, but it will be added to the bulk of the swine-flu vaccine being produced to stem a pandemic that health officials estimate could sicken more than a third of the state’s residents.

Pregnant women and young children are considered at high risk for swine flu, and lifting the mercury limits will give them quicker access to the vaccine, Selecky said.

“It’s vital that everyone in a high-risk group has the choice to be vaccinated when swine-flu vaccine becomes available,” she said.

About 15 percent of the vaccine supply will be mercury-free, but people may have to wait longer for it to become available.

U.S. Health and Human Services Secretary Kathleen Sebelius said Thursday that 6 million to 7 million doses of the vaccine will be available the first week in October, mainly in the form of a nasal spray called FluMist.

About 40 million flu shots should be ready by the middle of October, with an additional 10 million to 20 million doses rolling off the assembly lines every week after that for a total of 250 million doses.

“We will have enough vaccine to immunize every American who wants to be immunized,” Sebelius said in a briefing. “But it won’t all be available at the same time.”