The meeting, the first in a planned series, came amid new controversy about vaccines and autism - and a fledgling theory that vaccinations might worsen a rare condition called mitochondrial dysfunction that triggers certain forms of autism.

Federal health officials said that the work, which had been planned for two years, was not in response to that controversy and that it encompassed many more questions than autism - from rare side effects of the new shingles vaccine to how to predict who is at risk for encephalopathy sometimes triggered by other inoculations.

A government-appointed working group is charged with picking the most important safety questions for the Centers for Disease Control and Prevention to study over the next five years. What is unique is that the group also is supposed to get significant public input in setting those priorities, an effort to ease skepticism that authorities hide or discount important information about vaccines.

"A crisis of trust is going to be a crisis of public health," said Bruce Gellin, head of the National Vaccine Program Office.

"There's been a lot of anger and a lot of distrust over issues of vaccine safety," Andrew Pavia, a University of Utah pediatric infectious-disease specialist who is chairing the group, told the meeting yesterday.

"There's a need to engage as many voices as possible," he added. "It's a chance to make sure the right questions are going to be asked."

Numerous studies have addressed vaccines and autism and found no link, including with a once-common mercury-based preservative.

The newest question surfaced last month, with news that the government had agreed to pay the family of 9-year-old Hannah Poling for injuries linked to vaccines. Her family said Hannah was a healthy 19-month-old when she received five shots, nine vaccines in all. She became sick and later developed autism, and her parents filed a claim under the federal vaccine compensation act.

The government granted that claim late last year on the theory that the vaccines aggravated an underlying mitochondrial disorder, although federal health officials have insisted the compensation does not mean vaccines cause autism.

But the mitochondria question is on the list of top research questions the CDC made public yesterday. Hannah's mother joined other anti-autism advocates in pleading for it to begin.

A bigger issue for some of the government's advisers yesterday was what the CDC's proposed research agenda did not include - how many vaccines should be given in one visit, and if they are all really needed by age 2.

"We all have to have our kids vaccinated by the time they go into day care or kindergarten, but . . . does it all have to happen in the first two years?" asked panelist Christopher Carlson of the Fred Hutchinson Cancer Research Center, the father of a 9-year-old with a mild type of autism.

"I'm not saying there's proof one way or the other. But the lack of options is a concern I think we should think about."