Samantha Power, the Obama administration’s nominee for U.S. ambassador to the United Nations, told a Senate panel Wednesday that the world body’s failure to halt mass killing in Syria is a “disgrace that history will judge harshly.”

But Power voiced little optimism that China and Russia, key U.N. Security Council powers, can be persuaded to support decisive action on Syria. And she registered caution about the limits of U.S. power to respond to the world’s most tragic crises.

“I believe that America cannot — indeed, I know that America should not — police every crisis or shelter every refugee,” she said during a Senate Foreign Relations Committee hearing to consider her nomination. “While our goodwill knows no bounds, our resources are finite, strained by pressing needs at home. And we are not the world’s policeman. We must make choices based on the best interests of the American people.”

In an opening statement that highlighted her priorities and assessments of the strengths and flaws of the United Nations, Power praised the global body’s health workers as courageous in the face of terrorist threats in Nigeria and Pakistan while denouncing discrimination against Israel by member nations.

Power said that shielding Israel from unfair attacks by its political adversaries would be one of her top priorities. Others, she said, would include fighting U.N. corruption and waste, standing up against repressive regimes, and championing the cause of “human rights and human dignity.”

“The United States has no greater friend in the world than the state of Israel,” she said. “I will stand up for Israel and work tirelessly to defend it.”

Power invoked the names of two former U.S. ambassadors to the United Nations, Jeane Kirkpatrick and Daniel Patrick Moynihan, who had gained reputations for speaking forcefully against U.S. adversaries and despotic governments. Power said the United States’ defense of freedom would require “contesting the crackdown on civil society being carried out in countries like Cuba, Iran, Russia and Venezuela.”

“If I am given the privilege of sitting behind America’s placard, you will be able to count on me,” she said. “I will tirelessly promote and defend U.S. interests. I will be a blunt, outspoken champion of American values and of human rights.”

Power, an Irish-born immigrant who was raised in Atlanta, was introduced by Sens. Saxby Chambliss and Johnny Isakson, both Georgia Republicans.

Her prospects for confirmation were buoyed early on in the hearing when Sen. Bob Corker (Tenn.), the ranking Republican on the Foreign Relations Committee, suggested that he anticipated Power taking up the New York job. “I look forward to your service,” he said. “I think you’re going to be a significant and positive force at the United Nations.”

But Power faced some tough questioning from Republican senators, including Marco Rubio (Fla.), about remarks she made more than a decade ago about the United States’ and Israel’s role in the world.

Rubio pressed her to clarify remarks she had made in 2002 on a public access television program in Berkeley, Calif., about the possibility of imposing a political solution on Israel. Power was asked what advice she would offer an American president in a hypothetical scenario in which one of the parties to the Israeli-Palestinian conflict were on the verge of committing genocide. She answered that a credible response would require the imposition of “a mammoth protection force.” She also warned that pursuing such a course “might mean alienating a domestic constituency of tremendous political and financial import,” a reference to the pro-Israel lobby in the United States.

In response to Rubio, Power said, “I have dissociated myself from those comments many times,” adding, “I gave a long rambling and very remarkably incoherent response to a hypothetical question I should never have answered.”

She also backed away from the thrust of a 2003 article she wrote in the New Republic arguing that the United States needed to show greater remorse for its role in abetting massive crimes in the past, saying, “I probably very much overstated the case in that article.”

“There are things that I have written that I would write very differently today,” Power said, noting that she had probably written 1 million to 2 million words in her career as a foreign correspondent, Pulitzer Prize-winning author and scholar. “This country is the greatest country on Earth. I would never apologize for America.”