Gates was visiting Fort Greely which houses parts of the US anti-missile defense shield -- a land-based system with about 20 interceptors -- and said of Pyongyang that its "behavior has certainly alarmed people."
In the past Gates proposed slicing a billion dollars off the anti-missile system budget and freezing the development of interceptors at 30, instead of the 44 originally planned. But he indicated he might re-examine his proposal.
"My recommendation to the president was for the fiscal year 2010 budget, it's not a forever decision," the defense secretary said.
"And if capabilities in one of these rogue states should develop faster, or on a more worrisome way than anybody anticipates right now, then I think the way is opened in the future to add to the number of silos and interceptors up here."
There are fears North Korea is preparing to launch a long-range missile, after defying global condemnation of its second nuclear test last week by firing a series of short-range missiles.