FACTBOX-Possible successors to Indian PM Singh

NEW DELHI, March 7 (Reuters) - Indian Prime Minister Manmohan Singh, whose image has been tarnished by a series of corruption scandals, faces a fresh political test after a key coalition partner said it would pull out of the cabinet. Y

Singh, 78, is widely seen as holding the fort till Congress party heir apparent Rahul Gandhi takes over. But with Rahul showing no indications he is ready, any move by Singh to resign means party chief Sonia Gandhi will have to look among the most senior government ministers to fill the top post.

Here are some possible successors:

PRANAB MUKHERJEE

The No 2 in the cabinet, Finance Minister Pranab Mukherjee is Congress's main troubleshooter. While he is the most obvious candidate, one stumbling block in a party with a long memory is his expulsion from the Congress following a rift with Sonia Gandhi's late husband, Rajiv, in 1984.

Mukherjee, 75, is seen more as a political operator than a zealous economic reformer and this has been reflected in his budgets, which have catered to Congress's core rural and farmer voters.

PALANIAPPAN CHIDAMBARAM

Home Minister Chidambaram is one of the most reform-friendly and efficient ministers in the government, but his personal ambitions make many in the Congress wary.

The Harvard Business School-educated Chidambaram is not a political heavyweight, winning elections to parliament in 2009 by a slim majority.

India has seen a drop in militant attacks since the Mumbai attacks of November 2008 when he took up his post. But Chidambaram has been less successful tackling a Maoist insurgency that has raged in large parts of eastern and central India.

He has been a finance minister and a trade minister in earlier governments. His budgets have been hailed by corporates, with the 1997 edition being termed as a "dream budget" for slashing income, corporate and customs tax rates.

ARACKAPARAMBIL KURIEN ANTHONY

The 70-year-old defence minister is widely seen to be scrupulously honest, famously resigning on moral grounds as food minister in 1994 when his ministry was involved in a sugar import scandal, despite there being no allegations against him.

He has little visibility outside his southern home state of Kerala. While he is a self-proclaimed atheist, his Christian roots might be a drawback, given it could expose the Italian-born Catholic, Sonia Gandhi, to attacks from Hindu nationalists.

But as someone without lofty ambitions and with his clean image, Anthony is a perfect candidate to fill Singh's role as a stop-gap till Rahul decides to take over.

RAHUL GANDHI

The 40-year-old son of Congress chief Sonia has the prime ministership for the asking. But he has said he prefers to work on strengthening the party and has repeatedly declined to join the government.

Educated at Cambridge and Harvard, aides say he would want to be seen as earning the top job rather than as a member of the dynasty that has ruled India for 36 of its 63 years of independence.

Rahul is focused on reviving the Congress in its north Indian heartland, especially in Uttar Pradesh, the largest state which goes to polls in 2012. Any move to join the government will come only after that.

Rahul has spoken on the need for India's rapid economic growth to improve the lives of the poor. While he has said he favours policies that sustain that growth, many observers see him aligned to his mother's left-of centre political stance. kuncheria.jacob@thomsonreuters.com; +91 11 4178 1007; Reuters Messaging: kuncheria.jacob.reuters.com@reuters.net))