Sources close to Kalam told PTI that a formal announcement by the former President is expected very shortly.
Kalam conveyed his reluctance to contest when BJP leader L K Advani called him thrice to persuade him to be the Opposition's common candidate against UPA nominee Pranab Mukherjee, sources said.
Kalam, the predecessor to current President Pratibha Patil, told Advani that his "conscience" is not permitting him to contest, sources said.
BJP was trying hard to persuade him to contest, with Advani deputing his close aide Sudheendra Kulkarni to meet him twice today.
Kalam's candidature is being pushed by Trinamool Congress chief Mamata Banerjee, who broke ranks with UPA to prop him.
The former President has been insisting that he could consider entering the fray only if there was surety about his victory.
Several opposition leaders reportedly talked to Kalam over phone yesterday to know about his plans.
BJP was more in favour of fielding Kalam than former Lok Sabha Speaker P A Sangma, who is AIADMK Chief J Jayalalithaa and BJD head Naveen Patnaik's choice.
Even JD(U), which wants a consensus for Mukherjee, may support Kalam as he shares a good equation with Bihar Chief Minister Nitish Kumar.
