"The failure of the U.N. Security Council to respond to the slaughter in Syria is a disgrace that history will judge harshly," Power told the Senate Foreign Relations Committee.
But pressed by Sen. John McCain, she acknowledged that any forceful action was unlikely from an organization that, because of the veto power of Russia and China, hasn't penalized Syrian President Bashar Assad or even condemned his government's role in a 2-year civil war that has killed almost 100,000 people.
Moscow and Beijing have blocked U.S.-backed resolutions against the Assad government three times and remain opposed to any effort by Western and Arab countries to force Assad into stepping down.
Russia, however, says it is working with the U.S. to try to get Syria's government and rebels into peace talks.
Overall, the hearing amounted to a surprising show of bilateral backing for Power, a 42-year-old mother of two. She was a senior foreign policy adviser during Obama's first term and served as the first head of the Atrocities Prevention Board he established last year.
The top Republican on the committee, Sen. Bob Corker of Tennessee, declared himself "exceptionally excited" with Power heading to the United Nations, and Republican colleagues from Marco Rubio of Florida to McCain expressed their support.
But Rubio was the first of a few senators to raise several articles and interviews from Power's past. They included her 2002 call for a "mammoth protection force" to be dispatched to the Middle East to stem Arab-Israeli violence, and the suggestion a year later that the U.S. make a "historical reckoning" of its past crimes.
Rubio introduced legislation Wednesday to make America's hundreds of millions of dollars in annual contributions to the United Nations voluntary and give the U.S. the right to withhold funds for activities it finds objectionable.
Power said she long has dissociated herself from her call for an international protection force in the Mideast, calling it a "long, rambling and remarkably incoherent answer" to a hypothetical question she shouldn't have answered.
She said peace must come through a negotiated solution and that is why the administration is trying to get the Palestinians to drop their campaign for unilateral recognition as a state in multilateral organizations.
Pressed by Rubio on what specific crimes the U.S. has committed, Power, who was born in Ireland and moved to the U.S. as a child, repeated several times that she "would never apologize for America."
"America is a light to the world," she said, refusing to delve deeper into a 2003 article she wrote for The New Republic. She also rejected having ever referred to Iran's contested nuclear program as an "imagined crisis," as stated by Rubio.
Power, who would replace Obama's national security adviser, Susan Rice, at the U.N., said she'd seek to promote Israel at the United by helping it get one of the Security Council's rotating seats in 2018. It would mark Israel's first inclusion in the U.N.'s top decision-making body.
"The U.N. must be fair," Power said. "Israel's legitimacy should be beyond dispute, and its security must be beyond doubt. And just as I have done as President Obama's U.N. adviser at the White House, I will stand up for Israel and work tirelessly to defend it."
