WASHINGTON -- School-age children will be a key target population for a pandemic flu vaccine in the fall, and they may get their shots at school in a mass vaccination campaign not seen since the polio epidemics of the 1950s.

The federal government should get about 100 million doses of vaccine by mid-October, if the current production by five companies goes as planned. But enough vaccine for wide use by the 120 million people especially vulnerable to infection with the newly emerged strain of H1N1 influenza virus won't be available until later in the fall.

Those were among the messages that administration officials delivered to about 500 state, territorial, city and tribal health officials yesterday at a "flu summit" held at the National Institutes of Health's Bethesda, Md., campus.

President Barack Obama, speaking by audio link from the Group of Eight summit in L'Aquila, Italy, urged the audience to take "complete ownership" of preparations for the prospect of what he termed a "significant outbreak" of H1N1 flu in the next few six months.

"We want to make sure that we are not promoting panic, but we are promoting vigilance and preparation," he said, adding: "The most important thing for us to do is to make sure that state and local officials prepare now to implement a vaccination program in the fall."

Children between 6 months and 18 years old, pregnant women, adults with chronic illnesses and healthcare workers would likely be first in line for the pandemic flu vaccine, Health and Human Services Secretary Kathleen Sebelius told the gathering.

Secretary of Education Arne Duncan said "we would absolutely welcome" the idea that the nation's schools be a principal venue for delivering the shots. He called them "natural sites," and said that "to open our doors and be part of the solution really makes sense."

In recent years, some public school systems have offered seasonal flu vaccine to students. But there have been no school-based mass campaigns since the late 1950s, when children lined up to get the Salk vaccine "polio shot." How a 21st-century effort might be accomplished is an urgent priority of this summer's pandemic planning.

Vaccination campaigns, wherever they are held, would be mainly run by local governments. To help them make specific plans, Ms. Sebelius said the federal government would provide an additional $350 million, to be disbursed by the end of this month. About $260 million will go to states and territories, with the remaining $90 million going to hospitals to help them prepare for a likely surge of flu patients in their emergency rooms and intensive care units.

The federal government has spent about $1 billion so far on pandemic flu vaccine, with about $7 billion available for further purchases and other pandemic countermeasures.

The new H1N1 virus, derived from two strains of influenza virus that circulates in pigs, emerged in April in Mexico and southern California. Still called "swine flu" by many people, it is now in every state. More than 1 million Americans have become ill from it, and 170 have died. Worldwide, it is on every inhabited continent and responsible for at least 420 deaths.

Unlike seasonal flu, which typically strikes the elderly most severely, the new strain disproportionately attacks children and young adults. The tentative targeting of young people, however, will pose unusual challenges to the U.S. medical system, as many teenagers and young adults rarely visit doctors or clinics.