WASHINGTON (AP) — Scientists who sparked an outcry by creating easier-to-spread versions of the bird flu for research purposes want to try such experiments again using a worrisome new strain. This time around, the U.S. government is promising extra scrutiny of such high-stakes research up front.

Since it broke out in China in March, the H7N9 bird flu has infected more than 130 people and killed 43. Some of the world's leading flu researchers argue that genetically altering that virus in high-security labs is key to studying how it might mutate in the wild to become a bigger threat to people, maybe even the next pandemic.

"We cannot prevent epidemics or pandemics, but we can accumulate critical knowledge ahead of time" to help countries better prepare and respond, Ron Fouchier of Erasmus University in the Netherlands told The Associated Press.

In letters published Wednesday in the journals Science and Nature, Fouchier and colleagues from a dozen research centers in the U.S., Hong Kong and Britain outlined plans for what's called gain-of-function research — creating potentially stronger strains, including ones that might spread easily through the air between lab animals. They say the work could highlight the most important mutations for public health officials to watch for as they monitor the virus' natural spread or determine how to manufacture vaccines.

The announcement is an attempt to head off the kind of international controversy that erupted in 2011 when Fouchier and Yoshihiro Kawaoka of the University of Wisconsin, Madison, created easier-to-spread strains of another deadly kind of bird flu, the better-known H5N1. The concerns: How to guard against laboratory accidents with the man-made strains, and whether publishing findings from the research could offer a blueprint for would-be bioterrorists. The H5N1 work eventually was published.

Now the researchers aim to explain to the public ahead of time why they want to do more of this scary-sounding research, and how they'll manage the risks.

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The Obama administration already had tightened oversight of research involving dangerous germs. Wednesday, the U.S. Department of Health and Human Services announced an extra step: In addition to scientific review, researchers who propose creating easier-to-spread strains of the new H7N9 will have to pass a special review by a panel of experts who will weigh the risks and potential benefits of the work.

"There are strong arguments to do the science," but it has to be done properly or not at all, said Dr. Anthony Fauci of the National Institutes of Health, which will refer such projects to the special HHS panel.

"It's not a rubber stamp," Fauci said. "If the risk is felt to be too high by this outside review, they will recommend it won't be done and we won't fund it."

The extra oversight is for federally funded researchers; there is no way to know what privately funded research may be in the works.

The steps don't satisfy critics.

The findings from the earlier man-made H5N1 strains haven't changed how health authorities are monitoring that virus in the wild, said University of Minnesota professor Michael Osterholm, who was on the federal advisory board that first sounded the alarm over the issue. Nor is there scientific evidence that the mutations that seem most dangerous in the lab really could predict an impending pandemic.

"H5N1 surveillance is as haphazard today as it was two years ago," said Osterholm, who said Wednesday's announcement overstated the potential benefits of such research and minimized the risks. "Should we do the work if it's not actually going to make a difference?"

Scientists have anxiously monitored bird flu for years, but so far the deadliest strains of concern only occasionally sicken people, mostly after close contact with infected poultry. The H5N1 strain has sickened more than 600 people and caused 377 deaths, mostly in Asia, since the late 1990s.

Infections by its newly emerged cousin, the H7N9 virus, appear to have stalled since Chinese authorities cracked down on live animal markets. But scientists fear the virus will re-emerge in the winter, when influenza is most active. Chinese scientists announced this week that two of the earlier deaths included a woman who apparently caught the virus while caring for her ill father, the strongest evidence yet that it occasionally can spread among people.