NEW DELHI — India’s Prime Minister Manmohan Singh helped set his country on the path to modernity, prosperity and power, but critics say the shy, soft-spoken 79-year-old is in danger of going down in history as a failure.

The architect of India’s economic reforms, Singh was a major force behind his country’s rapprochement with the United States and is a respected figure on the world stage. President Obama’s aides used to boast of his tremendous rapport and friendship with Singh.

But the image of the scrupulously honorable, humble and intellectual technocrat has slowly given way to a completely different one: a dithering, ineffectual bureaucrat presiding over a deeply corrupt government.

Every day for the past two weeks, India’s Parliament has been adjourned as the opposition bays for Singh’s resignation over allegations of waste and corruption in the allocation of coal-mining concessions.

The story of Singh’s dramatic fall from grace in his second term in office and the slow but steady tarnishing of his reputation has played out in parallel with his country’s decline on his watch. As India’s economy has slowed and as its reputation for rampant corruption has reasserted itself, the idea that the country was on an inexorable road to becoming a global power has increasingly come into question.

“More and more, he has become a tragic figure in our history,” said political historian Ramachandra Guha, describing a man fatally handicapped by his “timidity, complacency and intellectual dishonesty.”

The irony is that Singh’s greatest selling points — his incorruptibility and economic experience — are the mirror image of his government’s greatest failings.

Under Singh, economic reforms have stalled, growth has slowed sharply and the rupee has collapsed. But just as damaging to his reputation is the accusation that he looked the other way and remained silent as his cabinet colleagues filled their own pockets.

In the process, he transformed himself from an object of respect to one of ridicule and endured the worst period in his life, said Sanjaya Baru, Singh’s media adviser during his first term.

Attendees at meetings and conferences were jokingly urged to put their phones into “Manmohan Singh mode,” while one joke cited a dentist urging the seated prime minister, “At least in my clinic, please open your mouth.”

Singh finally did open his mouth last week, to rebut criticism from the government auditor that the national treasury had been cheated of billions of dollars after coal-mining concessions were granted to private companies for a pittance — including during a five-year period when Singh doubled as coal minister.

Singh denied that there was “any impropriety,” but he was drowned out by catcalls when he attempted to address Parliament on the issue. His brief statement to the media afterward appeared to do little to change the impression of a man whose aloofness from the rough-and-tumble of Indian politics has been transformed from an asset into a liability.

“It has been my general practice not to respond to motivated criticism directed personally at me,” he said. “My general attitude has been, ‘My silence is better than a thousand answers; it keeps intact the honor of innumerable questions.’ ”