With barely three months to go, the race for the Indian presidency is heating up.

The country's former President A.P.J. Abdul Kalam's name currently figures at the top of the list which also includes Indian Vice President Hamid Ansari, veteran Finance Minister Pranab Mukherjee and Lok Sabha Speaker Meira Kumar.

The Indian President is elected by an electoral college consisted of the elected members of the two Houses of Parliament -- the Lok Sabha (Lower House) and the Rajya Sabha (Upper House), and Legislative Assemblies of the states.

Usually the ruling and the opposition parties agree to a consensual candidate for the presidency.

This time, while the ruling Congress party has been pitching for Ansari or Mukherjee for the ceremonial post, the country's main opposition Bharatiya Janata Party (BJP) has clearly ruled out supporting any Congressman for the position.

"We will not accept any Congress candidate, including Pranab Mukherjee, for the president's post," BJP's Leader of Opposition in Lok Sabha Sushma Swaraj told the media in the national capital Monday.

She also questioned Vice President Ansari's credentials for the top constitutional position, saying he "lacks stature".

Instead, the BJP came out in the open and almost backed the candidature of ex-president Kalam to succeed incumbent president Pratibha Patil whose tenure ends on July 25.

"If Mulayam Singh Yadav takes the name of Abdul Kalam then BJP can respond favorably. We are ok with Kalam but he has to agree to contest. Our party will never favour the candidature of Ansari and Mukherjee," Swaraj said.

She also ruled out any quid pro quo with Congress on the presidential election by accepting the vice president's post.

Mulayam Singh is the leader of Samajwadi Party, a regional party which recently swept to power in the northern state of Uttar Pradesh.

Experts say that Singh has emerged as a crucial swing factor in the contest to decide who gets to succeed Pratibha Patil in Rashtrapati Bhawan while BJP's decision not to support any Congress-backed candidate is linked to the party's plan for the 2014 general elections.

"They are looking at 2014 elections and do not want to give the impression that the BJP has any link with Congress," said Delhi- based Professor Ajay Singh, a political analyst.

The analysts say that the BJP's stand runs contrary to the assessment in certain quarters that the party might come around to support the Finance Minister Pranab Mukherjee because of his seniority and vast experience.

Another factor is the stand of regional Trinamool Congress party led by the eastern state of West Bengal's Chief Minister Mamata Banerjee.

"Little is known about her mind on this, except that she will meet Congress chief Sonia Gandhi this week," said professor SK Gupta, another expert.