The move was ordered by the 24th Air Force, which is responsible for maintaining Air Force computer networks. The Army, Navy and Marines aren’t blocking the sites, and the Defense Department hasn’t told the services to do so, according to spokespeople for the services and the Pentagon.

The Office of the Secretary of Defense has issued guidance against visiting WikiLeaks or downloading documents posted there, according to defense officials. The Air Force told its own personnel in August to avoid those actions. Service commanders have authority to go beyond Pentagon guidance and issue orders to protect classified information.

One senior defense official questioned the wisdom of blocking the newspaper sites or even prohibiting service members from visiting them on military computers, arguing that the information has spread on the Internet and that sites like the New York Times contain other, useful information.