Rebuffing criticism of the warm greetings he exchanged with Venezuelan leader Hugo Chavez, President Obama said Sunday that the United States, with its overwhelming military superiority and need to improve its global image, could afford to extend such diplomatic "courtesy."

In a news conference capping a three-day meeting of leaders from the Western Hemisphere, Obama also said the U.S. must engage other countries through humanitarian gestures, not only military intervention.

Obama said it would be a mistake to measure the Summit of the Americas by the specific agreements reached. By listening to his counterparts and eschewing heavy-handed diplomacy, he said, he was creating an atmosphere in which, "at the margins," foreign leaders are "more likely to want to cooperate than not cooperate."

A running theme of the summit was Obama's cordial dealings with Chavez, who once called former President George W. Bush the "devil" and who last month dismissed Obama as an "ignoramus." The two were photographed smiling and clasping hands.

At one meeting, Chavez made a show of walking around the table as the cameras rolled and handing Obama a copy of "Open Veins of Latin America," a 1971 book by Eduardo Galeano chronicling U.S. and European imperialism in the region.

Republican Sen. John Ensign of Nevada, appearing on CNN on Sunday, said it was "irresponsible" for Obama to be seen "laughing and joking" with the Venezuelan president.

Obama dismissed such concerns. He said the 2008 presidential campaign proved that American voters want the president to engage with his counterparts, whether or not they are avowed friends of the U.S.

He said it "was a nice gesture to give me a book. I'm a reader." The president added that the election was a referendum of sorts on the argument that U.S. solicitude toward foreign leaders could be seen as "weakness."

"The American people didn't buy it," Obama said. "And there's a good reason the American people didn't buy it, because it doesn't make sense."

The U.S. has nothing to fear from Venezuela, a large supplier of crude oil to the country, Obama said.

"Its defense budget is probably 1/600th of the U.S.," he said. "They own [the oil company] Citgo. It's unlikely that as a consequence of me shaking hands or having a polite conversation with Mr. Chavez that we are endangering the strategic interests of the United States."

That said, Obama aides were not so charitable toward Chavez. In a background briefing earlier, one senior official accused Chavez of performing for the cameras.

The official, who briefed reporters on the condition of anonymity, said, "Anybody who's been at international conferences with Chavez knows that if there's a camera around, he's going to find a way to get in it."

Apparently impressed with Obama, Chavez seemed ready to reevaluate relations with the United States. He announced that he was considering appointing an ambassador to Washington, an idea he discussed over the weekend with Secretary of State Hillary Rodham Clinton. The two countries expelled each other's ambassadors last year.

"We have a different focus, obviously," Chavez said on Venezuelan state television. "But we are willing. We have the political will to work together."

Though Cuba's fate was not on the official agenda of the summit, which included only democratically elected leaders from the hemisphere, many Latin American leaders pressed Obama to lift the United States' 47-year-old trade embargo on the island nation and normalize relations. Obama resisted.

His administration has already announced that it is loosening travel restrictions on Cuban Americans visiting family on the island. But at this point, Obama has refused to go further, calling upon Castro to move toward a more open and democratic form of government.

Lawrence H. Summers, the president's top economic advisor, said Sunday that the embargo would not end any time soon.

"That's way down the road, and it is going to depend on what Cuba . . . does going forward," Summers, who accompanied Obama on the trip, said on NBC's "Meet the Press."