* Full membership would tip balance of power in S.Asia
* Indian PM visits Switzerland, Mexico to seek backing
* Application of arch-rival Pakistan backed by China
* But China blocks India's effort to join 48-nation body (Adds Vienna meeting, details, paragraphs 1-2, 4-5)
By Frank Jack Daniel
MEXICO CITY, June 8 (Reuters) - Mexico supports India's efforts to join the Nuclear Suppliers Group (NSG), President Enrique Pena Nieto said on Wednesday, in a boost for Prime Minister Narendra Modi's diplomatic push to end his country's isolation over its nuclear arms programme.
India's bid to join the NSG is due to be discussed at a plenary session of the 48-member group in Vienna on Thursday.
"Mexico recognizes India's interest in joining the Nuclear Suppliers Group," Pena Nieto said, with Modi at his side at the Mexican president's Los Pinos residence. "As a country we have a positive and constructive backing for this."
India is also poised to join the Missile Technology Control Regime (MTCR) after talks this week between Modi and U.S. President Barack Obama in Washington.
Both groups would give India greater access to research and technology, but China has so far blocked Indias accession to the NSG.
Mexico supported India's membership because of Modi's "commitment to the agenda of nuclear disarmament and non-proliferation," Pena Nieto said.
New Delhi's bid for full membership, if granted, would tip the balance of power in South Asia against its arch-rival Pakistan, whose own application has been backed by China, despite questions over its proliferation record.
Pena Nieto's support is a boost for Modi, but he must still win China's support to seal India's membership of the non-proliferation body. The NSG holds its annual meeting in South Korea later this month.
"I thank President Pena Nieto for his positive and constructive support for India's membership of the Nuclear Suppliers Group," Modi said at the end of a whirlwind week of global diplomacy in which he also won support from Switzerland.
Mexico's backing represents a historic policy shift for the country, which has held a firm position on nuclear disarmament and non-proliferation for decades.
One of Mexico's crowning diplomatic achievements was the 1967 Treaty of Tlatelolco, which declared Latin America and the Caribbean a zone free of nuclear weapons.
India made its formal bid for membership last month after winning a waiver in 2008 allowing it to trade in commercial nuclear technology.
Modi tacked on Switzerland and Mexico as extra stops on a five-country tour to seek their support. (Reporting by Frank Jack Daniel; Editing by Simon Gardner, Clarence Fernandez and Paul Tait)