Prime Minister Atal Bihari Vajpayee's consensus-building talents are seen as the key factor that will propel the Bharatiya Janata Party-led National Democratic Alliance back into power.

But at 79, many wonder whether he is physically capable of another five-year term as prime minister, and this has fuelled speculation that the real candidate for premier is his deputy, L K Advani.

Although hardly a spring chicken himself at 76, Advani has long held the title among India's political and media pundits as Vajpayee's 'natural successor' to lead the world's largest democracy.

While questions about Vajpayee's health are seldom discussed in public, he has often hinted at early retirement. After the 1999 election, he said he would not run again, and in 2001 dramatically announced his resignation at a party meeting.

'Since I am the prime minister, I am responsible, he had said then. 'I have grown old. I am also unwell. I should leave the chair. That is why I have decided to resign.'

He later changed his mind after a flurry of leaders begged him to do so.

This time he has said he is contesting the election only out of fear that the Opposition would lead the nation into a state of 'anarchy.'

Now on an 8,000-kilometre (5,000 mile) yatra across the country, Advani is seen today as the front-runner for the job of prime minister after Vajpayee.

Analysts say while Vajpayee may be the face of the election -- figuring prominently on party posters and banners at every street corner -- Advani is the 'prime minister in-waiting.' The only question is timing.

"It (the succession) will happen only if Vajpayee faces a real threat to his health," analyst Yashwant Deshmukh said. "He will continue as long as his health allows or at least until the time of the Presidential election. Then he may pitch for the President's post. That's the best way for a glorious retirement."

The Presidential poll is not due till 2007.

"Vajpayee is here for as long as he wants. There's no question of him being eased out unless he goes on his own," said Mahesh Rangarajan, visiting assistant professor at the US-based Cornell University. He pointed out that in the past, elderly prime ministers with poor health had remained in the saddle.

At the same time, "Advani is a clear heir-apparent."

But there is a glaring contrast between the two leaders' images.

Vajpayee is a master orator, poet and long seen as the moderate face of the BJP. He also enjoys phenomenal personal popularity ratings, way above that of his party.

Advani, Vajpayee's one-time college roommate, is traditionally branded as hawkish and his speaking skills are more lacklustre. He was at the forefront of a virulent campaign a decade ago that united Hindu radical forces across the country in support of the temple movement.

However, ever since the Babri Masjid was demolished by Hindu fanatics, Advani has struggled to find widespread acceptance, especially among the country's estimated 13 crore (130 million) Muslims.

Of late, he has attempted an image makeover and tried to reach out to Muslims. He sought the blessings of a cleric of the Ajmer Sharif -- a prominent Sufi shrine in Rajasthan -- before embarking on his cross-country Bharat Uday Yatra.

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His efforts appear to have borne fruit over the past two weeks of campaigning as he has welcomed some Muslims into the BJP fold on the lawns of his Delhi home and some prominent Muslims were present at the start of his yatra.

It was in 2002 that Advani was officially made deputy prime minister after consultations with the two dozen-odd parties that form the NDA. "That was his litmus test," said Deshmukh. "Even the Opposition did not say anything. Now, if he is to be made the prime minister, there won't be any voice of dissent."