On the other, the chief justice continued, there is “the potential that a North Korean diesel electric submarine will get within range of Pearl Harbor undetected” if Navy personnel are not properly trained in the use of sonar.
“Now, I think that’s a pretty clear balance,” Chief Justice Roberts said.
Other justices also indicated an inclination to overturn a decision from the United States Court of Appeals for the Ninth Circuit, in San Francisco, imposing limits on the exercises, saying either that national security concerns trumped environmental ones or that judges are not competent to weigh the competing interests.
“I don’t know anything about this,” Justice Stephen G. Breyer said. “I’m not a naval officer.” But he said he was inclined to believe, in the absence of evidence to the contrary, a sworn statement from an admiral saying the restrictions would harm military preparedness.
Richard B. Kendall, a lawyer for the Natural Resources Defense Council, which had sued the Navy over the exercises, insisted that courts have an important role to play in protecting whales and dolphins even when the executive branch asserts a national security interest.
“The Navy cannot be judge of its own cause,” Mr. Kendall said.
The two sides agreed that sonar can harm marine mammals, but they disagreed about how much. Mr. Kendall said sonar produces noise as loud as 2,000 jet engines and that some whales die or become stranded in their frantic efforts to avoid it.
Gregory G. Garre, the United States solicitor general, said the impact on the animals was minor and passing. “They hear the sound, and they go in the opposite direction,” Mr. Garre said. “It can also mean that they could have some temporary effect on their feeding or breeding patterns.”
In a decision in February, the Ninth Circuit upheld a trial judge’s order that the Navy suspend the use of sonar if it detects a marine mammal within 2,200 yards and reduce sonar levels when water temperatures reach certain levels whether or not animals are present. The appeals court stayed its order until the Supreme Court decides the case, and the exercises are scheduled to conclude in January.
The precise questions before the court in the case, Winter v. Natural Resources Defense Council, No. 07-1239, were tangled. Is an agency called the Council on Environmental Quality — “more or less an office in the White House,” in Chief Justice Roberts’s words — permitted to override a court order? Did the lower courts use the wrong standard in entering an injunction? Must the environmental group prove harm to an entire species rather than to individual animals?
But at the heart of the case were arguments about the role of the courts in matters of national security. Judge Florence-Marie Cooper, of the Federal District Court in Los Angeles, had ruled that the Navy’s sonar training would not be compromised by the restrictions she imposed, a conclusion that Justice Samuel A. Alito Jr. seemed to find stunning.
“Isn’t there something incredibly odd,” Justice Alito asked, “about a single district judge making a determination on that defense question that is contrary to the determination that the Navy has made?”
“Is Judge Cooper an expert on antisubmarine warfare?” Justice Alito added a little later.
Mr. Kendall said Judge Cooper’s ruling was supported by ample evidence from experts and earlier training exercises.
Justice Breyer wondered whether the two interests involved — the environment and national security — could ever plausibly be reconciled.
“The whole point of the armed forces is to hurt the environment,” he said. “You go on a bombing mission — do they have to prepare an environmental impact statement first?”
Lisa Heinzerling, a law professor at Georgetown, said the environmental group, which sued under the National Environmental Policy Act, faced long odds. The Supreme Court has heard 15 cases under the act, she said, and the plaintiffs have lost all 15.
There are, moreover, Professor Heinzerling continued, “just not justices on the court for the most part who are out to save the whales.”
The court heard a second environmental case on Wednesday, Summers v. Earth Island Institute, No. 07-463, about who has standing to challenge Forest Service regulations. Several environmental groups sued the service in 2003 over a particular timber sale in the Sequoia National Forest in California called the Burnt Ridge project and over Forest Service regulations generally.
The question in the case was whether the plaintiffs may continue to pursue their general, or facial, challenge after reaching a settlement with the government in the Burnt Ridge matter. The Roberts court has looked askance at some facial challenges to statutes, and the tenor of the argument suggested that it will take a similar attitude here.