Three decades and two oceans stand between President Barack Obama and Prime Minister Manmohan Singh of India. But on a dais in New Delhi after a joint news conference on November 8, the two men, neither known for his social ebullience, were inseparable: the youthful, lanky American President's arm firmly fixed on the older man's shoulder, with Mr. Singh grinning widely and his arm wrapped tightly around Mr. Obama's waist.

More than once during his three-day visit Mr. Obama called the relationship between India and the United States “the defining partnership of the 21st century.” But the relationship between the two men has evolved into something of a friendship as well. Mr. Obama has called Mr. Singh his guru, and on November 8 Mr. Singh called Mr. Obama “a personal friend and a charismatic leader who has made a deep imprint on world affairs.”

Cold War to reconciliation

The long and complicated relationship between the United States and India has veered from warm embrace long before independence to the uneasy frostbite of the Cold War to the reconciliation of recent years, built on shared democratic and multicultural values and a desire to balance the influence of a rising China.

But even as broad historical forces have shaped the relationship, a personal bond appears to be forming between the leaders of the world's two largest democracies, who developed an easy rapport in their numerous international meetings and have now thrown state dinners for each other on reciprocal visits.

“The personal equation is very important,” said Ronen Sen, who until last year was India's ambassador to the United States.

Down the ages

President Dwight D. Eisenhower had a warm regard for India's first Prime Minister, Jawaharlal Nehru. When the President went to India in 1959, the two visited villages together in a convertible, and Eisenhower was greeted by adoring crowds everywhere he went.

Nehru's daughter, Indira Gandhi, who became Prime Minister in 1966, easily charmed President Lyndon B. Johnson that year on her first visit to the United States. He found the elegant, youthful woman irresistible, overstaying so long at a meeting at the home of Gandhi's cousin that he had to be invited to dinner.

Mrs Gandhi had notoriously noxious relations with President Richard M. Nixon. But when she and a newly elected President Ronald Reagan met in Cancun, Mexico, at a summit meeting on international development, they hit it off, to everyone's surprise. Mr. Reagan invited Mrs. Gandhi for a state visit, and she took him up on it.

The personal link

“In the height of the Cold War, because of personal chemistry, India and the United States managed to create a thaw in their frozen relations,” said Lalit Mansingh, a former foreign secretary and ambassador to the United States.

The Hindu nationalist party of Atal Bihari Vajpayee, India's Prime Minister from 1998 to 2004, had a centre-right ideology that fit well with that of President George W. Bush. The two men eventually began negotiating an agreement that would end India's nuclear exile.

Bush and Singh cemented that deal in 2005.

“They got on extremely well,” said Mr. Sen, the ambassador to the United States at the time.

At first glance it seemed to be an unlikely bond between the informal, back-slapping Mr. Bush and Mr. Singh, a reserved academic 14 years his senior. But Mr. Bush's deep interest in India impressed Mr. Singh, said officials who observed the relationship closely.

Sunanda K. Datta-Ray, an Indian journalist who has written a book about relations between the United States and India, said he, too, was surprised by the rapport between the two men and had asked Mr. Singh about it. Mr. Singh replied that he appreciated Mr. Bush's straightforward nature.

“He said he was a very warm and human person,” Mr. Datta-Ray said.

The Obama visit

Mr. Singh set tongues wagging when he told Mr. Bush, after a White House meeting, “The people of India love you deeply.” That Mr. Obama and Mr. Singh have found common ground is perhaps less of a surprise. Both are better at the intricacies of policy than at the glad-handing of politics. Both enjoy adulation on the global stage that seems to have eluded them at home.

Mr. Obama arrived in New Delhi fresh from his party's “shellacking” in a midterm-election cycle in which Democrats lost their majority in the House and saw their control of the Senate sharply narrowed.

Mr. Singh, a celebrated figure globally who was reappointed as Prime Minister when the Congress Party won parliamentary elections just a few months after Mr. Obama moved into the Oval Office, has faced harsh criticism at home for his handling of a crisis in Kashmir, rising food prices and perceived missteps in handling India's archrival, Pakistan. — © New York Times News Service

The long and complicated relationship has veered from warm embrace to uneasy frostbite to reconciliation.