TOKYO (Reuters) - Japan and China need "rules of the game" to keep a feud over tiny islands from escalating into a military clash, an adviser to Japan's prime minister said on Friday, as a ruling coalition partner prepared to visit Beijing in search of better ties.

Sino-Japanese ties chilled sharply after Japan bought the disputed islands in the East China Sea from a private Japanese citizen last September.

China scrambled two J-10 fighters last week in the area after two Japanese F-15s followed a Chinese military aircraft, which China said was on a "routine patrol".

Japan has sent up fighter jets several times recently to intercept Chinese planes near the islands, called the Senkaku by Japan and the Diaoyu by China.

Both sides have also sent patrol vessels to the area.

"We need some rules of the game. We have to discuss preventative measures," Shotaro Yachi, a former senior diplomat now advising Prime Minister Shinzo Abe on foreign policy told Reuters in an interview.

Yachi said he was very concerned about a possible unintended clash.

"During the Cold War, the United States and the Soviet Union had such 'rules of the game' to avoid a possible conflict. We can learn a lesson from their experience," he said.

Abe, who returned to the premiership after a five-year gap following his Liberal Democratic Party's (LDP) election win last month, has taken a tough stance in the row over the islands, vowing not to negotiate.

The dispute, which has coincided with a U.S. "pivot" in diplomatic and security focus to Asia, is hurting business ties between Asia's two biggest economies, creating pressure for some resolution.

COALITION PARTNER REACHING OUT

In a sign of a possible bid to reach out to China, Abe's coalition partner, Natsuo Yamaguchi, leader of the smaller, more dovish New Komeito party, is scheduled to visit China next week - perhaps carrying a message from the prime minister.

"There must be a tacit understanding between Mr Yamaguchi and the prime minister for seeking improved bilateral ties," Yachi said. LDP Vice President Masahiko Komura is also planning a China trip, though no dates have been set.

Still, a formula for resolving the dispute remains elusive, despite suggestions that the matter could somehow be "shelved" as historians say the two countries agreed to do decades ago.

"The situation now is that their government ships come to the adjacent zone and Japan's territorial waters and government airplanes invade Japan's airspace," Yachi said.

"We don't want to 'shelve' this situation."

On Friday, Abe wound up a trip to Vietnam, Thailand and Indonesia, part of a push for stronger ties with Southeast Asia to help counterbalance China's growing influence.

Japan is also talking to its key ally the United States about revising 15-year-old guidelines on defence cooperation while planning a make-over of its own long-term basic defence policy and bigger defence spending.

Yachi said some on the Chinese side were thinking in a "realistic and rational" way, so there was hope the two countries could engage. At the same time, a lack of transparency had left Tokyo guessing just what Beijing intends.

"We need to hedge. Maybe China will not go along with that (realistic and rational) policy, so we have to prepare.

"We have no intention to 'encircle' them, but if they come, we will respond. If they want to occupy the Senkaku islands, we have to respond. If they use military force, we have to respond effectively."

(Editing by Robert Birsel)

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