TOKYO (Reuters) - Japanese Prime Minister Shinzo Abe's push to revise the constitution to allow Tokyo's right to collective self-defence will pave the way for closer cooperation between US and Japanese forces in Asia, a top US commander said on Tuesday.

Expanded training and joint missions could extend across Asia from Japan through the disputed South China Sea - claimed in whole or part by China, Vietnam, the Philippines and other nations in the region - into the Indian Ocean.

Neither the United States nor Japan have territorial claims in the South China Sea, but the Seventh Fleet operates in the area. A Japanese naval presence there could irritate Beijing.

Lawmakers in Japan are set to approve Abe's constitutional reinterpretation to recognize Japan's right to collective self-defence (CSD). The Japanese parliament, where Abe enjoys a big majority, will vote on the new security legislation in May.

"CSD makes it easier for the Seventh Fleet and JMSDF (Japan Maritime Self-Defence Force) to exercise and operate across the Indo Asia Pacific," Admiral Robert Thomas, commander of the force said aboard his command ship, the USS Blue Ridge, in Yokohama.

The Japanese "have the capacity and capability for operations in international waters and international airspace anywhere on the globe," he told a media briefing with Admiral Eiichi Funada, commander of the JMSDF.

A broader regional military role for Japan is being welcomed by Washington, as it pushes its allies in Asia, including Australia, to do more as China takes an increasingly assertive stance in territorial disputes in the region.

Japan and the United State have said they will decide by the end of June on a new set of guidelines for their decades-old alliance that will give Japan a more prominent role.

The two admirals had earlier discussed expanding the scope of joint operations, in areas such as combating piracy and human trafficking and in human aid and disaster relief, Thomas said.

The two countries could also conduct training exercises in more diverse locations, he added.

The most powerful naval fleet in Asia, the US Seventh Fleet remains the main counterweight to China's growing maritime power in Asia. Centered around a carrier battle group that operates out of Japan, the US Seventh Fleet includes some 80 vessels, 140 aircraft and 40,000 sailors, making it the most powerful naval force in the western Pacific.

Japan's navy consists of around 120 vessels, including more than 40 destroyers and a submarine force of around 20 boats.