WASHINGTON — U.S. swine flu vaccinations could begin in October with children among the first in line — at their local schools — the Obama administration said Thursday as the president and his Cabinet urged states to figure out now how they'll tackle the virus's all-but-certain resurgence.

"We may end up averting a crisis. That's our hope," said President Barack Obama, who took time away from the G-8 summit in Italy to telephone another summit back home — the 500 state and local health officials meeting to prepare for swine flu's fall threat.

No final decision has been made on whether to vaccinate Americans, Health and Human Services Secretary Kathleen Sebelius stressed. That depends largely on studies with experimental batches that are set to start the first week of August — to see if they're safe and seem to work and to learn whether they require one or two doses.

But if all goes well, the federal government will buy vaccine from manufacturers and share it for free among the states, which must then "try and get this in the arms of the targeted population as soon as possible," Sebelius said.

First in line probably will be school-age children, young adults with risky conditions such as asthma, pregnant women and health workers, she said. Unlike regular winter flu, the swine flu seems more dangerous to these groups than to older people.

"Schools are natural places" to offer those vaccines, Education Secretary Arne Duncan said.

Go home and get schools, mayors and other community leaders to spread that message, Sebelius said.

"The last thing we want is millions of parents to be surprised" the day the get-your-kid-vaccinated-at-school note comes home, she said.

Schools do occasionally team up with local health officials for special flu vaccination clinics, but it's not common. More than 140 schools around the country scheduled flu vaccination days last fall, some providing free vaccine. Some vaccinated only students bearing parent consent forms; others opened their doors to entire families.

It will be a confusing fall, Sebelius acknowledged. Doctors' offices, clinics and even grocery stores will be in the midst of dispensing 100 million-plus doses of regular winter flu vaccine — and the swine flu vaccine, which will roll out slowly, will require at least one completely separate inoculation.

"We know a mass vaccination program of even modest scale will involve extraordinary effort on your part," Sebelius told state health workers.

She also announced $350 million in grants to help states prepare, money to be used partly to brace hospitals for a surge of demand from the truly sick and the well-but-worried.