After years of policy logjam and sleaze allegations, Singh´s administration burst into life last week when it announced a sudden blitz of reforms designed to revive the sharply slowing economy.[break]
Ahead of his expected retirement at the next elections, due in 2014, the plans have given his image a new boost with the Economic Times newspaper proclaiming he has got his "mojo back".
The prime minister spent the day with his family and at public engagements, including a speech to a science conference, his office said.
"There are no celebrations. He prefers to be with his family in the morning -- then work as usual," Singh´s spokesman told AFP.
Singh was credited with helping light the fuse for the nation´s rapid growth in 1991 when as finance minister he rescued an economy teetering on the brink of bankruptcy.
But his reputation has taken a battering since he returned as prime minister in 2004 -- and especially since the 2009 re-election of the Congress government -- with his administration buffeted by graft scandals.
Had Singh retired in 2009, history would have remembered him as a key architect of liberalisation "but unable to resist the lure of office he stayed on," renowned Indian historian Ramachandra Guha wrote Tuesday.
"In his second term, he has presided over what is arguably the most corrupt government in Indian history," Guha said in a column for the BBC, referring to the scandals that Singh failed to prevent or take swift action against.
Birthday greetings from Indian politicians flowed in on Tuesday and Russian President Vladimir Putin called Singh an "outstanding statesman" in a personal message.
"You have earned well-deserved respect as an outstanding statesman and eminent economist," said Putin, whose country enjoys close ties with India even as New Delhi´s relationship with the United States has blossomed.
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