WASHINGTON  The Supreme Court sided with the White House on Monday in two cases involving national security and worries about the environment, strengthening the Bush administration’s drive, at least for now, for sweeping executive powers in the post-9/11 world.

In one case, the court refused to stop the administration from bypassing environmental reviews in building a security fence along the border between the United States and Mexico. In the other, it agreed to hear the administration’s appeal of a lower court decision that, on environmental grounds, restricted the Navy’s use of powerful sonar off the Southern California coast. .

In the sonar case, the justices said they would review a decision by the United States Court of Appeals for the Ninth Circuit, which on Feb. 27 upheld most of a lower court ruling that banned high-powered sonar within 12 miles of the coast. Environmental groups had sued to block the use of the sonar because they feared harm to whales and dolphins.

The Bush administration has argued that the sonar training exercises, used to practice tracking of hostile submarines, are vital to national defense, that the possible harm to marine life was being exaggerated and that, in any event, military need should take precedence over the welfare of water creatures.