GENEVA — Global health ministers agreed today to put off setting a deadline to destroy the last known stockpiles of the smallpox virus for three more years, rejecting a U.S. plan that had called for a five-year delay.

After two days of heated debate, the 193-nation World Health Assembly agreed to a compromise that calls for another review in 2014.

The United States had proposed a five-year extension to destroying the U.S. and Russian stockpiles, arguing that more research is needed and the stockpiles could help prevent one of the world’s deadliest diseases from being used as a biological weapon.

But many ministers at the decision-making assembly of the World Health Organization said they saw little reason to retain the stockpiles, and objected to the delay in destroying them.

The assembly declared smallpox officially eradicated in 1980, and the U.N. health agency has been discussing whether to destroy the virus since 1986.

Then in 2007, the assembly asked WHO’s director-general to oversee a major review of the situation so that the 2011 assembly could agree on when to destroy the last known stockpiles.

WHO officials said in a statement that the assembly “strongly reaffirmed the decision of previous assemblies that the remaining stock of smallpox (variola) virus should be destroyed when crucial research based on the virus has been completed.”

But the assembly won’t again have to grapple with a decision over exactly when to do that until three years from now.

The assembly, like the U.N. General Assembly, is a world forum whose decisions aren’t legally binding but do carry moral weight. So even if the assembly finally sets a date for destroying the stockpiles, it can’t force the United States and Russia to comply.