Congress had a poor showing in December state polls

The main opposition Congress party on Tuesday called the move an act of "unprincipled opportunism" by the BJP.

Prime Minister Atal Behari Vajpayee vowed to go to the polls "at the earliest" after a BJP resolution on the issue at a party forum in Hyderabad.

The BJP wants polls as early as April, capitalising on recent state election successes and improved Pakistan ties.

An early poll would have to be approved by the Election Commission, an autonomous body.

Election preparations will start after the cabinet recommends that the parliament's lower house be dissolved

It is a sign of [BJP] weakness Harkishan Singh Surjeet, communist leader

Congress senior leader Kapil Sibal accused the BJP of breaking convention.

"It is the prerogative of the prime minister to dissolve the house, but what we question is the level of opportunism that has made the BJP do this at present," Mr Sibal said.

However, he said, Congress was ready for polls "any time" and was finalising electoral alliances.

India's communist parties have also criticised the BJP decision.

"It is a sign of their weakness," Communist Party of India (Marxist) general secretary Harkishan Singh Surjeet told the AFP news agency.

'Big battle'

Another top communist leader, AB Bardhan, said that never before had parliament "been dissolved because a political party thinks it has a good chance to win elections".

"Under what pretext are they planning early elections?" he asked.

Mr Vajpayee wants to cash in on the "feel-good" factor

"There is no challenge to Vajpayee's majority in parliament, the country is under no threat."

Mr Vajpayee told his party in Hyderabad: "The hour of deciding has come... I hope a new government will be in place by April. A big battle lies ahead. The situation is in our favour."

Mr Vajpayee has asked his finance minister to prepare a national spending provision because the country's budget will not be passed in time.

This will help wrap up parliamentary business before dissolution.

'Feel-good factor'

The BJP has a number of elements in its favour for an early election.

The Indian economy is growing at a rate of 7% to 8% per year on the back of a good monsoon and record industrial production.

The stock markets are at a new high, and so are the foreign exchange reserves, at more than $100bn.

A recent visit to Pakistan and an agreement for talks on the disputed region of Kashmir has also boosted Mr Vajpayee.

India's national elections take around six weeks to complete.