US officials said Washington and Moscow have both been working with Kazakhstan to build up defenses against Iran in the Caspian and in its western military district.
"We're cooperating," Rumsfeld told a joint news conference in Astana with Kazakh Defense Minister Mukhtar Altynbayev.
"(It is) important to this country and to the world that the security be assured in that area," he said, referring to the Caspian.
Only Russia and Iran currently have navies in the Caspian, leaving Kazakhstan with little military means to protect its oil reserves.
A consortium of western oil companies reached an agreement with the Kazakh government Wednesday that is expected to clear the way for production at the Kashagan oil field in the northern Caspian by 2008.
Kashagan is the largest field that Kazakhstan has let out for development since the discovery of huge reserves following the breakup of the Soviet Union.
The government estimates that exploiting the field will require some 29 billion dollars in investments.
Altynbayev said his government and the United States had a five-year program for military cooperation that encompasses Caspian security as well as other issues, such as combating the proliferation of weapons of mass destruction and drug trafficking.
"We are interested in getting assistance for providing security in the Caspian region," he said through an interpreter.
The United States has supplied Kazakhstan with Humvees and UH-1 "Huey" helicopters in an effort to help make its military more mobile, as well as building materials for new barracks and offices being constructed in the western military district, officials said.
"We're trying to get them to spend serious money on helicopters," a US official said.
Naval patrol craft and radar to strengthen control of Kazakhstan's land and maritime borders also are possibilities, a senior US defense official said.
NATO also is providing technical assistance to Kazakhstan's efforts to protect its Caspian Sea oil.
"We have exercises, various types of equipment, refurbishment of bases," Rumsfeld said.
But a US military education and training program has stalled, pending a State Department certification that Kazakhstan is making progress on economic and political reforms, US officials said.
Rumsfeld traveled to Kazakhstan from Uzbekistan, which also faces a break in funding for US military education and training programs unless the State Department certifies it has made progress on reforms.
Both former Soviet Republics are ruled by autocrats with poor human rights records.
But Rumsfeld praised both for their support for the US war on terrorism.
He met here with a group of 15 military engineers who recently returned from Iraq, where they served with the Polish-led multinational division as ordnance disposal experts.