By Jon Herskovitz

JOHANNESBURG (Reuters) - South Africa's deputy president left for China on Monday on a trip that Beijing may use to influence Pretoria to reject a visa application by the Dalai Lama.

South Africa has not made a decision yet to allow a visit by the Tibetan spiritual leader and Nobel Peace Laureate, the Foreign Ministry said. The Dalai Lama was invited by Archbishop Desmond Tutu, another Peace Prize recipient, to attend his 80th birthday celebration in early October.

The Dalai Lama, once embraced as a beacon of peace in South Africa when apartheid ended, has become a diplomatic headache for the country as its economic fortunes are increasingly linked to China, which had pushed Pretoria to reject a previous visa application.

The three-day visit by South African Deputy President Kgalema Motlanthe is aimed at bolstering economic ties. He was invited by Vice President Xi Jingping, widely seen as China's future leader.

In mid-July, Xi, in his first major speech on Tibet, vowed to crack down on separatist forces he said were led by the Dalai Lama, suggesting he will not ease Beijing's hardline stance toward the region and angering many Tibetan self-advocacy groups.

"It is a concern not to upset the Chinese," said Thomas Wheeler, a diplomacy specialist at the South African Institute of International Affairs.

South Africa rejected the Dalai Lama's last application when Tutu and former Presidents Nelson Mandela and F.W. de Klerk invited him to a 2010 peace conference.

"When you are dealing with the reality of politics, there are other considerations than these high principles. That has been a let down for everybody who expected South Africa to be different," Wheeler said.

South Africa exports about $5.5 billion a year in minerals to China and Africa's largest economy has been increasingly a destination for Chinese foreign direct investment.

China last year invited South Africa to join the BRIC grouping, a diplomatic coup for President Jacob Zuma. It was also seen by analysts as a Chinese stamp of approval for the country's role as a stepping stone to the African continent.

China has ruled Tibet with an iron fist since Communist troops marched in 1950. It says its rule has brought much needed development to a poor and backward region.

(Reporting by Jon Herskovitz)