"For this institution to become an engine of change in the 21st century it must now change itself," Rice told the opening meeting of the annual U.N. General Assembly special session.
"The United Nations must launch a lasting revolution of reform," she said in prepared remarks for her first U.N. speech.
Rice singled out human rights deficiencies and terrorism as immediate problems to take on. Terrorism is the greatest threat confronting the world, she said.
"No cause, no movement, and no grievance can justify the intentional killing of innocent civilians and noncombatants," Rice said in urging adoption of a sweeping anti-terrorism convention
She rejected arguments raised by some groups that terrorism often exists in the eye of the beholder, and that one man's terrorist is another man's freedom fighter.
Preceding Rice to the rostrum, Secretary-General Kofi Annan said condemnation must be unqualified and that the 191 countries should "forge a global counterterrorism strategy that weakens terrorists and strengthens the international community."
"We can do it, and we must," Annan said.
Rice's speech reflects a determination by the Bush administration to refashion the U.N., which has fallen far short of completing major changes sought by Annan.
Rice has locked arms with the secretary-general, declaring him an effective manager with whom she can work closely. The speech to the General Assembly conveys their joint effort to update the U.N. beyond the watered-down, 35-page reform document approved Friday.
"I have never had a better relationship with anyone than Kofi Annan," Rice said this week, thereby separating U.S. concerns about management flaws from the world body's top diplomat.
In her speech, Rice called the document a useful first step, but no more than that. The administration seeks, for instance, to exclude countries with poor human rights records from sitting in judgment of other nations. It also wants the secretary-general to have the flexibility to make wholesale changes in personnel.
The U.S. delegation, headed by reform-minded Ambassador John R. Bolton, never reluctant to point out U.N. shortcomings even at the risk of irritating traditional diplomats, is expected to follow up Rice's recommendations with resolutions in the coming weeks.
President George W. Bush, in his speech this week to the U.N., tried to motivate adoption of measures to counter poverty by linking poverty with terrorism. He listed a number of countries that have suffered at the hands of terrorists, and the United States succeeded in deterring moves to exempt national liberation movements from being branded as terrorist groups.
While reform was the centerpiece of her speech, Rice also dealt with world trouble spots, especially Iran's refusal to negotiate with the European Union an end to activities that suggest it is developing nuclear weapons.
"Secretary of State Rice made clear in her remarks that the U.S. favors a referral of Iran to the Security Council for sanctions if negotiations fail," said CBS News Foreign Affairs Analyst Pamela Falk from the U.N. "because the Bush Administration suspects that Iran's uranium enrichment program is a nuclear weapons program, but the resistance from Russia and China to vote for sanctions, may undermine a U.S. referral."
Iran, meanwhile, has challenged the administration to produce evidence that it is in violation of international standards in its nuclear activities. President Mahmoud Ahmadinejad planned to rebut the U.S. position in his own speech Saturday.
Rice scheduled seven meetings with foreign officials. She has held limited sessions, leaving New York twice during the week to assist Bush in White House meetings.
History's largest gathering of world leaders fell far short of completing the bold changes U.N. Secretary-General Kofi Annan sought to fight poverty, terrorism and human rights abuses — but the leaders took a first step.
At the end of a three-day summit, the leaders on Friday adopted a 35-page document by consensus after Venezuela made a formal reservation. When Swedish Prime Minister Goran Persson banged the gavel signifying approval, the leaders burst into applause.
The summit's approval of a modest document, which commits governments to achieving U.N. goals to combat poverty and creates a commission to help move countries from war to peace, came alongside important developments in other areas.
"After a week of acrimonious negotiations, the U.S. agreed to a final statement on terror, poverty and human rights," said Falk from the U.N., "but the real agendas were negotiated behind closed doors, including possible sanctions on Iran for uranium enrichment programs, the future of Iraq, the Haitian elections in November and who will be the next Secretary General after Kofi Annan's term ends in late 2006."
"The advantage of having all the Heads of State in a three-day summit in this General Assembly session was a great advantage over previous U.N. meetings," said Falk, "because of the ability to have so many bilateral meetings."