OSLO, Norway - President Obama delivered an impassioned rationale for war in accepting the 2009 Nobel Prize for Peace yesterday, a paradox that he acknowledged even as he defended America's record abroad in promoting human rights, individual freedom, and global security.

Just over a week after announcing an escalation of the U.S. war effort in Afghanistan, Obama spoke candidly to an audience that included European dignitaries and officials representing countries deeply opposed to the conflict. He did not receive applause until more than halfway through his speech - and even then not for his defense of "just war" but for his decision to close the military brig at Guantanamo Bay, Cuba, and prohibit torture.

The remarks offered a lofty, ideological justification for his decision to send an additional 30,000 U.S. troops to Afghanistan, and stood in sharp contrast to the more technical argument he made in favor of escalation last week at the U.S. Military Academy at West Point. His audience reached beyond the vaulted ceilings of Oslo City Hall to electorates in the United States and Europe, where many believe the war is no longer worth fighting.

While the president invoked the Rev. Dr. Martin Luther King Jr. and called himself "living testimony to the moral force of nonviolence," Obama also recalled the advance of Hitler's armies during World War II to argue that, sometimes, only force can resolve injustice and protect civilian lives. In an echo of his predecessor, George W. Bush, he noted that "evil does exist in the world."

"I face the world as it is, and cannot stand idle in the face of threats to the American people," Obama said in the speech, formally known as the Nobel Lecture. "To say that force may sometimes be necessary is not a call to cynicism. It is a recognition of history: the imperfections of man and the limits of reason."

The apparent contradiction of a wartime president accepting a prize for peace provided the fulcrum for Obama's 36-minute acceptance speech, which he delivered to about 1,000 people, including Norway's royal family and top government officials.

But Obama also used the speech to acknowledge the criticism that, less than a year into his presidency, he is undeserving of a prize that has been given to "Schweitzer and King, Marshall and Mandela."

After receiving the award with "great gratitude and great humility," Obama reminded the audience that he is "at the beginning, and not the end, of my labors on the world stage" and cited rights activists around the world who "have been jailed and beaten in the pursuit of justice."

"I cannot argue with those who find these men and women - some known, some obscure to all but those they help - to be far more deserving of this honor than I," he said.

Politically, the White House was careful not to play up Obama's award, what with so many families hurting economically at home and more troops heading off to war. Quite a few Norwegians were said to be miffed that he stayed but a day, not the usual three, and skipped a number of traditional events.

The award consists of a diploma and a gold medal bearing the etched face of Alfred Nobel, the wealthy chemist and inventor of dynamite who endowed the prize more than a century ago. It carries a $1.4 million cash award, which the White House has said Obama will donate to charity. At least some of the money, White House press secretary Robert Gibbs has said, might go to a group focused on microfinance, the development specialty of Obama's mother.

During the speech, Obama reprised foreign policy themes that he has spelled out previously, including the importance of working through the international organizations in an age of nuclear proliferation and environmental threats.

Some of Obama's collective appeals for global unity are beginning to show tentative results, including a more concerted approach by China, India, and the United States to address climate change; a stronger international response to Iran's and North Korea's nuclear programs; and NATO's recent pledge of thousands of additional troops to Afghanistan. But the president warned that the "old architecture" that the United States helped establish after World War II - from the United Nations to global treaties - is "buckling under the weight of new threats," including transnational terrorism and the rising instance of civil war.

Since taking office with a pledge to turn the page on the Bush administration's unilateralism, Obama has been criticized by conservatives for attempting to engage American adversaries, including those with poor human-rights records, with fresh diplomacy.

But yesterday, he cited the governments of Myanmar, Zimbabwe, and Iran for political repression, while warning that "human rights cannot be about exhortation alone" and "at times, it must be coupled with painstaking diplomacy."

In remarks to reporters before his address, Obama reiterated his commitment to begin withdrawing U.S. troops from Afghanistan in July 2011.

"The pace at which that takes place, the slope of a drawdown, how it occurs tactically, those are all going to be conditions-based," Obama said. "We're not going to see some sharp cliff, some precipitous drawdown."