By Sanjoy Majumder BBC News Online correspondent in Delhi

BJP state victories last year: Can success be repeated nationally?

The polls were due to have been held by October at the latest.

Most of the voting will be staggered over four separate days, starting on 20 April and ending on 10 May.

Counting is on 13 May.

The move by Prime Minister Atal Behari Vajpayee's ruling Bharatiya Janata Party to hold the polls ahead of schedule comes as no surprise.

The BJP and its allies are hoping to translate a series of recent political and economic triumphs into an election victory.

Analysts say the BJP will not wish to risk being hurt by a poor monsoon this year, which usually hits India after June

The prime minister recently concluded successful talks with India's long-time rival Pakistan.

In a breakthrough, the two sides have restarted a peace process stalled from the first half of Mr Vajpayee's five-year term.

The move is a personal triumph for the prime minister who had initiated peace moves as early as 1999.

Pakistan's President, Pervez Musharraf, publicly acknowledged Mr Vajpayee's role in sealing the peace plan.

Opposition disarray

Both the BJP and its allies are keen to use the elderly Mr Vajpayee's personal popularity in the campaign, particularly against an opposition that is increasingly in disarray.

Mr Vajpayee is seeking a place in the history books

The party is also hoping to continue the momentum after state election victories in December.

The BJP ousted its main rival, the opposition Congress Party, from three out of four states where it was in power, all in the politically influential northern and central belt.

It left many questioning the leadership qualities of Congress leader Sonia Gandhi, who is relatively inexperienced in politics.

While Mr Vajpayee has successfully managed a coalition of more than 20 parties ranging from socialists to the far-right, Congress is still trying to put together an effective alliance to challenge the BJP.

'Feel good' factor

But perhaps the biggest incentive for early elections is India's booming economy.

With foreign exchange reserves of more than $100bn, a rising stock market index and an economic growth rate around 8%, the Vajpayee government wants to tap in on what's being described as the "feel good" factor.

An excellent monsoon in 2003 led to increased farm production as well as huge gains for industry, particularly the car-makers, and pharmaceutical and software companies.

Analysts say the BJP will not wish to risk being hurt by a poor monsoon this year, which usually hits India after June.

Indian business also favours early polls since it is unlikely tough economic steps will be taken by a government in an election year.

Indeed, recent weeks have seen a series of new measures, such as tax cuts, which most people have taken to be attempts to increase the government's popularity.

Prime Minister Vajpayee is in the twilight of his political career - he turned 79 last month - and has been politically active for more than half a century.