HANOI (AFP) -- As Vietnam's communist rulers this week map out strategies for the next five years, they will keep in mind the need to balance relations with two geopolitical giants, the United States and China.

Vietnam must find ways to nurture ties with both the old and the rising superpower, without upsetting either, analysts say.

The communist party, which holds its five-yearly congress from Tuesday until April 25, can traditionally count on political ally China, whose model of tight political control and open markets it has emulated.

But booming Vietnam is also reliant on its former battlefield enemy and ideological foe the United States as it seeks to integrate into the global economy and join the World Trade Organisation (WTO) this year.

In the generation since the 1975 fall of Saigon, former U.S. president Bill Clinton visited Vietnam in 2000, and in 2005 Phan Van Khai became the first post-war Vietnamese prime minister to make the trip to Washington.

President George W. Bush is due in Hanoi for an Asia Pacific Economic Cooperation (APEC) summit in November.

The two sides have even resumed military ties and restarted their human rights dialogue. Last week U.S. Republican House Speaker Dennis Hastert said he would give Vietnam the thumbs up in its bid to join the WTO this year.

None of this has gone unnoticed in Beijing.

"The U.S. has been seriously paying attention to how to compete with China for influence in Asia," said Shi Yinhong, professor of international relations at Renmin University in Beijing. "China has no reason to tell Vietnam not to develop relations with the United States. But if Vietnam develops relations with the U.S., especially strategic relations, of course China would have a certain level of concern."

Ties have historically been tense between Vietnam and China, which has repeatedly invaded and been expelled from its small southern neighbor. Chinese troops last attacked in 1979 in a brief war both sides claimed to have won.

But relations have warmed again since 1991, and today pragmatism rules. Chinese politburo member Jia Qinglin visited Hanoi in March, followed by a trip this month by Defense Minister Cao Gangchuan.

"The neighborly China-Vietnam friendship has stood the test of time and keeps making new progress," Wu Bangguo, chairman of China's National People's Congress Standing Committee, told the official Xinhua news agency.

"Developing the China-Vietnam friendship complies with the interests of both countries and peoples benefits peace and development in the region and the world at large," Wu was quoted as saying.

Can Hanoi play both games? It has to, say analysts.

Vietnam must develop ties with Asian economic powerhouse China, but it also banks heavily on investment and trade with the United States, the world's largest economy. "Vietnam does not want a confrontation with either China or the U.S.," said Nguyen Anh Tuan of the Vietnamese Foreign Ministry's Institute of International Relations. "Its interest is to balance its ties with these two powers."

The diplomatic high-wire act has triggered fierce debate within the party, where some old revolutionaries remain deeply distrustful of the West.

"Those in charge of the economy say... getting access to the US market is worth making all these concessions for," said Carl Thayer, a Vietnam expert at the Australian Defence Force Academy. "To that extent, they are pro-US. They see enormous benefits for Vietnam. The concessions that they made then become in some circles the object of attacks for conceding too much to the US." "There are those who trust the United States at face level to a certain extent and those who have very, very deep suspicions that the US is still trying to democratize Vietnam and invest it in an anti-China containment strategy."