Federal officials on Tuesday ended a moratorium imposed three years ago on funding research that alters germs to make them more lethal.

Such work can now proceed, said Dr. Francis S. Collins, the head of the National Institutes of Health, but only if a scientific panel decides that the benefits justify the risks.

Some scientists are eager to pursue these studies because they may show, for example, how the bird flu could mutate to more easily infect humans or could yield clues to making a better vaccine.

Critics say these researchers risk creating a monster germ that could escape the lab and seed a pandemic.

Now, a government panel will require that researchers show that their studies in this area are scientifically sound and that they will be done in a high-security lab.

The pathogen to be modified must pose a serious health threat, and the work must produce knowledge — such as a vaccine — that would benefit humans. Finally, there must be no safer way to do the research.

“We see this as a rigorous policy,” Dr. Collins said. “We want to be sure we’re doing this right.”

In October 2014, all federal funding was halted on efforts to make three viruses more dangerous: the flu virus, and those causing Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome (SARS).

But the new regulations apply to any pathogen that could potentially cause a pandemic. For example, they would apply to a request to create an Ebola virus transmissible through the air, said Dr. Collins.

There has been a long, fierce debate about projects — known as “gain of function” research — intended to make pathogens more deadly or more transmissible.

In 2011, an outcry arose when laboratories in Wisconsin and the Netherlands revealed that they were trying to mutate the lethal H5N1 bird flu in ways that would let it jump easily between ferrets, which are used to model human flu susceptibility.

Tensions rose in 2014 after the Centers for Disease Control and Prevention accidentally exposed lab workers to anthrax and shipped a deadly flu virus to a laboratory that had asked for a benign strain.