FACTBOX: What's at stake in India's giant general election

(Reuters) - Indians began voting on Thursday in a staggered general election that will end on May 13. Results are due on May 16.

The main battle is between the Congress-led coalition government and the main opposition bloc, headed by the mainstream Hindu nationalist Bharatiya Janata Party (BJP).

Here are some of the key issues at stake in the outcome.

ECONOMY

Investors fear a weak or unstable coalition government could emerge as the country grapples with the effects of the global economic slowdown and layoffs.

Business wants, but may not get, a strong government to push ahead with a quick raft of reform policies -- such as privatizations and relaxation of labor laws -- that stalled in five years of Congress rule, and impose fiscal discipline.

Many of Congress' attempts at reforms were blocked by its former communist partners who may once again join a ruling alliance.

Investors would largely welcome the return of the main opposition, pro-market BJP, which pushed liberalization and privatization until it lost power in 2004.

Investors also worry about the rise of a group of smaller, regional parties known as the "Third Front" who are presenting themselves as an alternative to the two giant blocs, and widely seen as an unknown quantity if they come to power.

SECURITY

India is still tense after a string of militant attacks last year, including a rampage on Mumbai that killed 166 people in November and spiked tensions with nuclear-armed Pakistan.

Under Congress, India pressed the pause button on a slow-moving peace process with Pakistan after Mumbai and says relations will improve only if Islamabad gets serious on clamping down on militants operating on its soil.

The BJP has accused its main rival of being soft on militancy and Pakistan. The party has shown signs of being more hawkish than Congress but proved pragmatic in dealing with India's neighbor when in power.

A new government needs also to deal with a long-running Maoist insurgency which has killed thousands since it began in the 1960s. The BJP has hinted it would be tougher on insurgents.

Again, if the Third Front comes to power it may be weaker or unpredictable in the way it deals with security threats.

INDIA ON THE WORLD STAGE

Congress' prime minister, the economist Manmohan Singh, is credited with liberalizing India's socialist economy in the 1990s which led to years of economic boom and made India an emerging giant on the world stage.

A weak coalition government, unable to press ahead with economic reforms, may slow India's rise and may prove to be an obstacle in its fight to revive economic growth and compete with China.

Relations with the United States improved both under BJP and Congress rule. Singh signed a civilian nuclear deal with Washington last year, taking India out of decades of nuclear isolation and paving the way for the country to meet its bulging energy needs.

But Congress' former leftist allies, who are suspicious of the United States, walked out of the coalition over the deal, and may damage ties with Washington if they return to hold the balance of power in parliament.

RELIGIOUS TENSION

In this election, the BJP has been criticized for playing too strongly its Hindu nationalist card -- the concept of "Hindutva" that sees India as more of a Hindu than secular nation.

A win by the BJP will reignite fears of religious tensions similar to what was seen in the BJP-run state of Gujarat in 2002, in which hundreds of Muslims were killed by Hindu mobs.

The BJP says it believes in equal treatment of all sections of Indian society, and points to Muslims that are members of its party.

(Compiled by Matthias Williams; Editing by Alistair Scrutton and Sanjeev Miglani)