NEW DELHI (Reuters) - Often seen as an honest but ineffectual man, Indian Prime Minister Manmohan Singh proved his toughness when he secured his government's survival and stood firm over a nuclear deal with the United States.

But Singh did not escape unscathed from Tuesday's closely fought confidence vote, with a bribery scandal threatening his squeaky clean image.

He admitted he was "extremely sad" after opposition lawmakers accused his government of bribing them to abstain.

"He was challenged, he was abused, all sorts of things were said, but he has come out victorious," said B.G. Verghese, author and commentator. "It is a great moral, political victory."

Singh's reputation was forged in his time as finance minister in the 1990s, when he pushed through a series of economic reforms which set the stage for India's subsequent boom and entry onto the world stage as a rising economic power.

But he seemed an unlikely choice for prime minister, thrust into the limelight only because Sonia Gandhi, head of the Congress party, turned down the top job after winning elections in 2004.

Time and again, Singh seemed dwarfed by Gandhi and ill-suited to the rough and tumble of Indian politics. He seemed to reach a nadir last year when his communist allies forced him to back down over the nuclear deal.

Singh had staked much of his prestige on the deal, shaking hands with U.S. President George W. Bush on first announcing it at the White House in 2005.

He was visibly crestfallen when forced to back down last year, as his cabinet colleagues were not prepared to face early elections.