The announcement, which was made by the White House Office of Science and Technology Policy and the Department of Health and Human Services, did not say how long the moratorium would last. It said a “deliberative process to assess the potential risks and benefits” would begin this month and stretch at least into next year.

The move appeared to be a sudden change of heart by the Obama administration, which last month issued regulations calling for more stringent federal oversight of such research and requiring scientists and universities to disclose that their work might be risky, rather than expecting federal agencies to notice.

Critics at the time dismissed those rules as too weak.

The moratorium is only on research on influenza virus and the coronaviruses that cause SARS and MERS. It made no mention of Ebola or any related filovirus. Ebola is already extremely lethal, but it is not easily transmissible.

No scientist has publicly announced an attempt to make Ebola as easy to transmit with a sneeze as flu is. Given the current panic around Ebola, and congressional anger at federal health agencies, it is unlikely that federal funding for such a project would be given out.

The debate over the wisdom of “gain of function” research erupted in 2011 when the labs of Ron Fouchier of Erasmus University in the Netherlands, and Yoshihiro Kawaoka of the University of Wisconsin-Madison, separately announced that they had succeeded in making the lethal H5N1 avian flu easily transmissible between ferrets, which are a model for human susceptibility to flu.