The U.S. Bureau of Land Management granted permission yesterday to the Marine Corps to conduct two weeks of military exercises in the Arizona desert in late April and early May. Environmentalists are worried that tortoises and rare desert plants might be casualties of the Marine exercises. Known as Desert Scimitar ’02, the mission will test the ability of the Marines to deploy large numbers of troops and equipment (some 600 vehicles and 2,700 personnel) over terrain similar to that of the Middle East. The BLM said it was “proud” to provide the land to the Marines, who have promised not to run over reptiles and plants with their Humvees, armored personnel carriers, and five-ton trucks. The Marines also will not be allowed to work at night, engage in live or simulated firing, or stray from established roads and paths. Still, biologists worry that dust kicked up by the 600 vehicles could cause serious long-term harm to plants and animals.