WASHINGTON — The Supreme Court on Monday rejected the government’s broad use of an exemption in the federal Freedom of Information Act to withhold documents from the public, ruling for a Washington state resident who wants Navy maps relating to its main West Coast ammunition dump.

The court,

by an 8-1 vote, threw out an appeals court ruling that backed the Navy’s decision to withhold maps showing the extent of damage expected from an explosion at the ammunition dump near Port Townsend in western Washington.

Justice Elena Kagan, writing for the court, said maps could not be withheld under a FOIA provision that deals with a federal agency’s “personnel rules and practices.” Kagan said that part of the law concerns “issues of employee relations and human resources.”

Justice Stephen Breyer dissented, saying the courts have consistently allowed broad use of the exemption for 30 years. “I would let sleeping dogs lie,” Breyer said.

The case before the court revolved around competing ideas of public safety. The government said that releasing the maps could allow someone to identify the precise location of the munitions that are stored at its base on Indian Island.

But Glen Milner, a longtime community activist, said that the people who live near the base have valid reasons for wanting to know whether they would be endangered by an explosion. An explosion at the Navy’s Port Chicago ammunition depot during World War II killed 320 people.

Milner has raised safety concerns about several area naval facilities. While he could not get the map for the ammunition dump, an official at an area submarine base provided Milner a map showing the probable range of damage from an explosion at that facility.

Kagan said the Navy may have legitimate interests in keeping the maps out of public circulation. She said the government could stamp the maps “classified,” which would keep them from being disclosed under FOIA. Or the Navy could perhaps rely on another FOIA provision that protects law enforcement information in some circumstances, she said.

The Associated Press is among 20 news organizations that filed a brief urging the court to limit the government’s invocation of the personnel exemption.

The case is Milner v. Department of the Navy, 09-1163.