NEW DELHI (Reuters) - India’s Prime Minister Manmohan Singh underwent successful coronary bypass surgery on Saturday, while confusion surrounded who was in charge of government just months before a general election.

The 76-year-old leader will be in hospital for at least a week and may be able to return to work in a month, doctors involved in his operation said.

“The entire country is rejoicing because our Prime Minister Dr. Manmohan Singh has come out ... successfully from the operation,” ruling Congress party general secretary Veerappa Moily told reporters.

Singh’s operation came just as his Congress party prepares its re-election campaign for a general election by May.

No acting prime minister has been named while Singh is in hospital.

Some officials said Foreign Minister Pranab Mukherjee would take over most prime ministerial responsibilities, including defense, security and the finance portfolio, while Singh was recovering from surgery.

“Pranab Mukherjee is in charge of the government until the prime minister resumes his duty,” an official in the prime minister’s office, who asked to remain anonymous, told Reuters.

“This is normal procedure as he is the most senior member of the cabinet, so there has been no official announcement.”

But a government spokesman insisted this was not the case.

India's Prime Minister Manmohan Singh speaks during a conference on development, freedom and welfare in honour of Indian Nobel economics laureate Amartya Sen in New Delhi December 19, 2008. REUTERS/B Mathur

“The prime minister is still in charge,” he told Reuters. “Nobody has taken over his functions.”

Moily told local media: “There cannot be two prime ministers and under the constitution, there can only be one prime minister.”

“NO CLARITY”

That confusion was mirrored in the media, where some papers and television channels said Mukherjee was in charge but others disagreed.

“Nobody named in charge,” the Mail Today announced on its front page. “No clarity on who controls the nukes.”

The confusion led to speculation the ruling Congress party did not want to give Mukherjee a public endorsement as acting prime minister just before an election, and overshadow other candidates within Congress battling to be Singh’s successor.

Rahul Gandhi, heir to one of India’s most powerful family dynasties, is emerging as a potential successor, media reports said.

Singh has been expected to continue as prime minister if the Congress coalition wins the general election. The main battle is between the Congress-led government and a coalition led by the Hindu-nationalist Bharatiya Janata Party.

A soft-spoken economist, Singh does not play an important role in election rallies, so analysts said the impact of his absence on the Congress party’s chances may be limited.

Singh underwent bypass surgery in 1990 in Britain. He also underwent wrist surgery in 2006, prostate gland surgery and a cataract removal procedure last year, officials said.

Across India, hundreds of Indians prayed for him at temples.

Pakistan President Asif Ali Zardari and Prime Minister Yousaf Raza Gilani sent bouquets of flowers to the prime minister. India’s relations with Pakistan have been tense since attacks in Mumbai in November which killed 179 people.

In neighbouring Bhutan, hundreds of Buddhist monks held special prayers for the Indian prime minister.