In a not-so-subtle dig at the Bush administration, US Ambassador Susan Rice said Wednesday the United States has paid the price for "stiff-arming the UN" and spurning international partners and is now embarked on a new era of global engagement. A key to this new engagement is a dramatic new approach to the United Nations, she said. Setting the stage for US President Barack Obama's first address to the UN General Assembly in September, Rice called the 192-nation organization "vital to our efforts to craft a better, safer world" because "so many of America's security interests come together today at the United Nations." She never mentioned the Bush administration and its difficult and sometimes antagonistic relationship with the UN, especially when John Bolton was ambassador. But her speech at New York University's Center for Global Affairs, released by the US Mission, highlighted the differences in tone and actions under Obama. Rice said the change in US approach to the UN is essential because of the "extraordinary array" of global security challenges in the 21st century. She cited poorly guarded nuclear weapons and material, the global financial meltdown, wars in Iraq and Afghanistan, a build-up of nuclear weapons capabilities by North Korea and Iran, terrorist acts by al-Qaida and its affiliates, genocide, cyber attacks, international crime and drug trafficking, pandemics, and global warming. These challenges cannot be tackled alone, Rice said, and the Obama administration believes that while US leadership is necessary, the "effective cooperation" of a broad range of friends and partners is essential. She cautioned that the US has "no illusions" about the UN's shortcomings, singling out the Security Council stumbling over issues such as Darfur, Zimbabwe and Myanmar, the General Assembly unfairly focusing on Israel, and the UN system needing to "confront waste and abuse even as it struggles to meet daunting new responsibilities for peacekeeping, humanitarian assistance and development." Reiterating Obama's statement that the UN is imperfect but indispensable, Rice stressed that "there can be no substitute for the legitimacy the UN can impart or its potential to mobilize the widest possible coalitions." She said there is also no better alternative to sharing the burdens and costs of UN peacekeeping and humanitarian operations - and "there is no doubt that we are more secure when the UN can foster nonproliferation and promote disarmament." "In short, the UN is essential to our efforts to galvanize concerted actions that make Americans safer and more secure," Rice said. Since she arrived at the UN, Rice said the US negotiated a resolution with tough new sanctions against North Korea for conducting a second nuclear test. It has also joined the Human Rights Council, embraced UN anti-poverty goals "which the United States previously shunned," rescinded a ban on US assistance to programs that support family planning and reproductive health services, resumed US funding for the UN Population Fund and signed the UN Convention on the Rights of Persons with Disabilities, she said. The United States also reversed course and backed a General Assembly statement opposing violence and discrimination based on sexual orientation, and it no longer opposes mentions of the International Criminal Court or "the right to food," Rice said, "and we are forging a new path on climate change commensurate with our responsibilities." She said in addition to the vast array of challenges the US inherited, there will be new ones, and inevitably there will be setbacks, frustrations and differences that remain intractable. "But we've seen the costs of disengaging," she said. "We have paid the price of stiff-arming the UN and spurning our international partners." "The United States will lead in the 21st century - not with hubris, not by hectoring, but through patient diplomacy and steadfast resolve to strengthen our common security by investing in our common humanity.