An opinion poll has predicted the coalition led by Prime Minister Atal Behari Vajpayee will retain power.
The main contest is between Vajpayee's Hindu nationalist Bharatiya Janata Party and Italian-born Sonia Gandhi led Congress Party, which has ruled India for 42 of 57 years of independence, but has been in opposition for eight years.
The last date for filing nominations is March 31.
Of the total 543 constituencies, 139 will go to polls during the first phase of balloting on April 20.
Polling for two seats in violence-wracked Tripura state will be held in the second phase on April 22.
A total of 675 million voters are eligible to vote on April 20, 22, 26, May 5 and May 10 in the largest franchise exercise in the world. The votes will be counted on May 13.
The polling is staggered to ensure sufficient security at each polling site.
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