WASHINGTON, Dec. 27 - The Defense Department, which controls 28 million acres of land across the nation that it uses for combat exercises and weapons testing, has been moving on a variety of fronts to reduce requirements that it safeguard the environment on that land. In Congress, the Pentagon has won exemptions in the last two years from parts of the Endangered Species Act and the Marine Mammal Protection Act. It has sought in recent years to exempt military activities, for three years, from compliance with parts of the Clean Air Act. Also, the Pentagon, which controls about 140 of...