The United States plans to produce a new strain of anthrax to test the effectiveness of its vaccines against the deadly biological agent, the Pentagon said today.

Work to produce the strain has not yet begun, but administration lawyers have concluded that it would be permitted under a 1972 global treaty that bans biological weapons but allows research for defensive purposes, Pentagon spokeswoman Victoria Clarke said.

Clarke said the anthrax project was devised in response to a 1997 report in the scientific journal Vaccine on a new anthrax strain believed to have been developed by the Russians through genetic engineering.

"We have a vaccine that works against a known anthrax strain. What we want to do is make sure we are prepared for any surprises, for anything that might happen that might be a threat," she said.

The plan calls for producing a small quantity of the strain for testing purposes, she said.