SINGAPORE, Sept 6 (Reuter) - Singapore's Senior Minister Lee Kuan Yew has warned of dangers in a deteriorating relationship between the United States and China, saying differences should not be allowed to progress too far.

In an article written for the New York Times and carried in Wednesday's Straits Times newspaper, the Singapore patriarch warned that "China is serious about using force if Taiwan threatens to become independent."

"Any shift in the U.S. one-China policy which appears to condone or encourage two Chinas or one China and one Taiwan will be seen as a threat to China's territorial integrity," the former Singapore prime minister wrote.

He said differences over trade, investment and open markets do not challenge China's unity and territorial integrity, but those "over democracy and human rights, if pushed too far, will. Any encouragement of independence for Tibet or Taiwan is 'casus belli', that is, cause for war."

Most East Asians want the United States to maintain a presence in the region and do not want to have to choose between China and Japan, Lee wrote.

"Will an industrialised and strong China be as benign to Southeast Asia as the U.S. has been since 1945? Singapore is not sure. Neither are Indonesia, Malaysia, the Philippines, Thailand and Brunei, the other countries in ASEAN (the Association of Southeast Asian Nations)."

China is "more self-assured and willing to take tough positions," but it is also more willing to accept foreigners and foreign ideas and for the next two decades "badly needs capital, technology, know-how and markets," Lee said.

He said: "It would be infinitely better if the U.S. and China do not lock horns. Then the U.S. and China will enjoy the full benefits from the fast-growing economies of the rest of the Asia-Pacific."