Is it ethical for a media outlet to hide a story?

I was reading an article about how the US funded Pakistan's nuclear program. Although most people are focusing on whether was right for the US to another country's nuclear program, something else caught my eye:

The New York Times has known details of the secret program for more than three years, based on interviews with a range of American officials and nuclear experts, some of whom were concerned that Pakistan’s arsenal remained vulnerable. The newspaper agreed to delay publication of the article after considering a request from the Bush administration, which argued that premature disclosure could hurt the effort to secure the weapons.

This brings me to a more important question: it it ethical for a media outlet to hide a story? I read the NY Times and trust that it gives me the most up to date news. If they wrote about the program, would it have jeopardized national security or would it have improved the program? Read the entire article here.