Gates took on Ma's claims that China wants only to defend itself with intercontinental ballistic missiles and is focused on defensive systems.
"I don't know what you use them for if it's not for offensive capabilities," Gates told reporters Sunday. While that kind of system might be considered a deterrent for other countries, Gates said it is "clearly for use in an offensive way."
He also dismissed China's protests about U.S. plans for an anti-missile defenses with Japan, as well as the deployment of missile defense sites in Poland and the Czech Republic.
Ma did not mention the United States by name, but said there are concerns in Pacific about the expansion of missile defense that could create instability in the region.
Asked about Ma's comments, Gates said, "I think that it's more of a political statement than it is one about military strategy."
U.S. and Chinese officials have taken slow but measurable steps to improve relations, including establishing a hot line between the countries' defense agencies. The Chinese also have offered thanks for U.S. aid after the recent earthquake in Sichuan province.
Tensions remain, however, leading to concerns the countries will build up their militaries in an effort to counteract and compete with each other.
In recent weeks China and Russia issued a joint statement condemning U.S. missile defense plans. Washington has struggle to convince both countries that the missile interceptors are not a threat to them.
The U.S. system, Gates said, is designed to defend against a small number of incoming missiles and would be overwhelmed easily "should a country with scores, if not hundreds of missiles, launch an attack."
Gates said the U.S. was concerned about China's expanding military. Officials are watching developments closely and "we will make our own adjustments as necessary," he said.
Ma said China's military spending was "limited and proportional."
"China's defense expenditure is at a low level in contrast to some developed countries in the world," Ma said during an international security conference in Singapore over the weekend. "We are military threat to no other country."
Amid all the rhetoric, Gates said he is pleased with recent meetings between the two countries, including a private session with Ma on Saturday.
"Our hope is that over the next year or two this dialogue will develop in a way that enables us both to avoid unnecessary military expenditures," Gates said.
