The 1972 treaty forbids nations from developing or acquiring weapons that spread disease, but it allows work on vaccines and other protective measures. Government officials said the secret research, which mimicked the major steps a state or terrorist would take to create a biological arsenal, was aimed at better understanding the threat.
The projects, which have not been previously disclosed, were begun under President Clinton and have been embraced by the Bush administration, which intends to expand them.
Earlier this year, administration officials said, the Pentagon drew up plans to engineer genetically a potentially more potent variant of the bacterium that causes anthrax, a deadly disease ideal for germ warfare.
The experiment has been devised to assess whether the vaccine now being given to millions of American soldiers is effective against such a superbug, which was first created by Russian scientists. A Bush administration official said the National Security Council is expected to give the final go-ahead later this month.
Two other projects completed during the Clinton administration focused on the mechanics of making germ weapons.
In a program code-named Clear Vision, the Central Intelligence Agency built and tested a model of a Soviet-designed germ bomb that agency officials feared was being sold on the international market. The C.I.A. device lacked a fuse and other parts that would make it a working bomb, intelligence officials said.
At about the same time, Pentagon experts assembled a germ factory in the Nevada desert from commercially available materials. Pentagon officials said the project demonstrated the ease with which a terrorist or rogue nation could build a plant that could produce pounds of the deadly germs.
Both the mock bomb and the factory were tested with simulants — benign substances with characteristics similar to the germs used in weapons, officials said.
A senior Bush administration official said all the projects were ”fully consistent” with the treaty banning biological weapons and were needed to protect Americans against a growing danger. ”This administration will pursue defenses against the full spectrum of biological threats,” the official said.