LUCKNOW, India, April 13 (Reuters) - Polling began on Friday for the second of a seven-phase election in India's heartland state of Uttar Pradesh, seen as an indicator of the popularity of two major national parties ahead of 2009 general elections.

The month-long election process kicked off with the first day of polling on April 7. Counting of votes is due on May 11.

Elections have been staggered in the sprawling state -- which has a population greater than that of Russia and Australia combined -- to enable adequate deployment of security forces in all areas of the province where past polls have seen violence.

More than 16 million voters are expected to cast their vote across nearly 16,000 polling booths in constituencies largely in the western part of the state on Friday.

Nearly 900 candidates are in the fray for the second phase which would elect 58 lawmakers to a 403-seat legislature.

Two state-wide parties supported by lower castes are running neck-and-neck in opinion polls, but neither is expected to win an outright majority.

With national elections two years away, pundits will also scrutinise the performance of the main national opposition, the Bharatiya Janata Party (BJP), likely to emerge as the third largest party in the state and a potential coalition partner.

The country's ruling Congress party has long struggled in Uttar Pradesh and is trailing a distant fourth place in polls. But after a disappointing spell as a junior coalition partner in the state, it could find itself completely excluded from power.

That would be a symbolic blow for Prime Minister Manmohan Singh and his Congress-led national government, already under national pressure from rising inflation and controversy about reforms meant to boost foreign investment and industrialisation.

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