NEW DELHI (Reuters) - Sonia Gandhi, India's ruling Congress party chief and the country's most powerful politician, will undergo surgery abroad, possibly in the United States, for an undisclosed medical condition and could be out for two to three weeks.

The absence of the 64-year-old figurehead of India's most prominent family dynasty may further hamper the Congress-led coalition government, which is already seen as rudderless amid a raft of corruption scandals and public fury over high inflation.

It could also accelerate the rise of her son, Rahul, one of a quartet of people appointed to take charge while she is away and considered to be India's prime minister-in-waiting.

"Generally her condition is satisfactory but her operation has not taken place as yet," Janardan Dwivedi, a general secretary of the party, told reporters.

In a sign of the confusion amid the surprise announcement, Dwivedi first told reporters that she had already undergone surgery, before correcting himself. He said the surgery would be abroad and local media said it could be in the United States.

The Italian-born Gandhi is the leading figure of a family that has ruled the country for much of India's independence, holding together the biggest national party through electoral troubles and scandals in this country of 1.2 billion people.

Her leftist leanings have proved a strong influence over a government officially led by the more reformist Prime Minister Manmohan Singh and she has pushed pro-poor policies such as food subsidies and guaranteed employment for villagers.

She nominated Singh as prime minister in 2004 and is widely considered to be more powerful than him, governing India from behind the scenes from her leafy bungalow in the capital, New Delhi.

Her son Rahul has increasingly taken on a national political role, gaining headlines for his defense of farmers protesting land acquisition for industry and infrastructure and seen as a champion of the poor visiting small hamlets and spending the night in villages.

"It is rather unusual. But it looks like a move to prepare Rahul Gandhi for his ultimate coronation," said Amulya Ganguli, a political analyst.

Sonia Gandhi's family has been at the tragic center of India's history. Her husband, Rajiv, and mother-in-law Indira, were both assassinated. Indira Gandhi's father, Jawaharlal Nehru, was India's first prime minister.

The daughter of a Turin builder who married into India's first family more than 30 years ago, Gandhi swept to power in 2004 on a wave of anger among the country's hundreds of millions of poor, who voted out the Hindu nationalist government after feeling left out of an economic boom.

Despite being re-elected in 2009, the Congress party-led government has suffered from a string of corruption scandals and high food inflation, and her leadership has been increasingly questioned as being out of touch.

(Additional reporting by Rajesh Kumar Singh, Manoj Kumar, Annie Banerji and C.J. Kuncheria; Writing by Alistair Scrutton; Editing by John Chalmers)