WASHINGTON — International scientists who last year halted controversial research with the deadly bird flu say they are resuming their work as countries adopt new rules to ensure safety.

The outcry erupted when two labs — in the Netherlands and the U.S. — reported they had created easier-to-spread versions of bird flu. Amid fierce debate about the oversight of such research and whether it might aid terrorists, those scientists voluntarily halted further work last January — and more than three dozen of the world’s leading flu researchers signed on as well.

On Wednesday, those scientists announced they were ending their moratorium because their pause in study worked: It gave the U.S. government and other world health authorities time to determine how they would oversee high-stakes research involving dangerous germs.

A number of countries already have issued new rules. The U.S. is finalizing its own research guidelines, a process that Dr. Anthony Fauci of the National Institutes of Health said should be completed within several weeks.