WASHINGTON  The Air Force is barring its personnel from using work computers to view the Web sites of The New York Times and more than 25 other news organizations and blogs that have posted secret cables obtained by WikiLeaks, Air Force officials said Tuesday.

When Air Force personnel on the service’s computer network try to view the Web sites of The Times, the British newspaper The Guardian, the German magazine Der Spiegel, the Spanish newspaper El País and the French newspaper Le Monde, as well as other sites that posted full confidential cables, the screen says “Access Denied: Internet usage is logged and monitored,” according to an Air Force official whose access was blocked and who shared the screen warning with The Times. Violators are warned that they face punishment if they try to view classified material from unauthorized Web sites.

Some Air Force officials acknowledged that the steps taken might be in vain since many military personnel could gain access to the documents from home computers, despite admonishments from superiors not to read the cables without proper clearances.

Cyber network specialists within the Air Force Space Command last week followed longstanding procedures to keep classified information off unclassified computer systems. “News media Web sites will be blocked if they post classified documents from the WikiLeaks Web site,” said Lt. Col. Brenda Campbell, a spokeswoman for the Air Force Space Command, a unit of which oversees Air Force cyber systems. “This is similar to how we’d block any other Web site that posted classified information.”