What better way to celebrate a birthday than to take to the world stage? Last week, Hu Jintao became the first Chinese president to address the U.N. General Assembly, a privilege seemingly reserved for the U.S. president and colorful despots such as Moammar Gadhafi. The People's Republic, which turned 60 on Thursday, has evolved from tin-pot polity to powerhouse. And among the spectacular transformations China has undergone, its dramatic turnabout in how it relates to the world stands out.

China began as a pariah state, rejected by and hostile toward the world community. Marxism shaped its view of international organizations as the "instruments of capitalist imperialism and hegemonism," and for decades China had little to do with them.

Fast-forward to last week, when Hu proclaimed the "important role" of the United Nations and entreated the international community to "continue our joint endeavor to build a harmonious world of enduring peace and common prosperity."

Today, China has joined every major international organization to which it is eligible and signed more than 300 international treaties. It even has had a hand in creating new regional groups.

"They are acting like the new us," a U.S. official told me.

China prepares, sends huge delegations to summits and carefully cultivates diplomatic capital. And this is not just lip service. In many cases, China's engagement with global entities such as the World Trade Organization and the International Monetary Fund has prompted Beijing to bring its conduct in line with international standards.

The next step, though, is an important one. Now that China is fully engaged and has earned considerable clout, what will it do? Will it increasingly abide by and support international standards? Could it eventually become a genuine leader for the global common good, with the risk and sacrifice that often entails?

Beijing sends mixed signals. On the hopeful side, we see China's leadership on the North Korean nuclear issue — playing host to many rounds of the six-party talks, producing draft agreements and now, for the first time, enforcing U.N. sanctions against its nominal ally. And although it once objected to the whole idea, China now has 2,000 of its citizens in U.N. peacekeeping operations.

China also has done an about-face since the 2003 SARS debacle, when it covered up the outbreak and deceived international health officials. This time, it is sponsoring international conferences on swine flu and vaccinating millions of its people. In the economic realm, the stimulus package Beijing enacted in response to the global meltdown was huge — exactly the scale that the IMF and the U.S. recommended.

Of course, every nation acts in its own interests, but in all these cases, China also promotes the broader safety and prosperity of the world.

However, other areas show the zero-sum side of China's international engagement. On climate change, China is one of the big bumps in the road on the way to a binding treaty at the Copenhagen summit in December. Thankfully — as it is now the world's largest emitter of carbon dioxide — Beijing is going gangbusters on efficiency standards and renewables. But unless those domestic ambitions can be turned into specific and verifiable international commitments, there will be no deal, and the world will continue toward climate calamity.

There are other concerns. Chinese companies are signing billion-dollar energy contracts with Iran just as the international community is trying to ratchet up the pressure on the Tehran regime over its nuclear ambitions. And Beijing is still holding out against tougher sanctions as the U.S., France, Britain and even Russia push forward.

Also, China's human-rights conduct does not live up to international standards, and, often to ensure access to natural resources, it supports and shelters dictators who abuse their people. Its concerted efforts at industrial espionage undermine international law, and its no-strings-attached development assistance, while doing some good, is setting back anti-corruption efforts.

The U.S. does not have the power to make China a global do-gooder, but it has some cards to play. Administration officials have begun to frame the bilateral relationship in terms of global challenges, so that the health of the U.S.-China relationship, which Beijing cares deeply about, is tied to progress on major threats such as climate change and Iran. The U.S. is also re-engaging with multilateral organizations, which increases Washington's leverage when dealing with Beijing.

One of the most effective ways for Washington to shape China's evolution is to remove Beijing's excuses for inaction by leading ourselves — passing strong climate change legislation, ratifying the Comprehensive Test Ban Treaty, making good on President Obama's disarmament pledges and increasing efforts to alleviate extreme poverty around the globe.

U.S. exceptionalism often has provided political cover to China. In his own speech to the United Nations last week, Obama acknowledged that the U.S. hasn't always been a fully responsible superpower, and he pledged to do better.

The Chinese say it is unfair to expect a still-developing China to shoulder so much international responsibility. But the forces of globalization that made China the major power it is today are the same ones breeding threats that only nations acting in concert can address.

China has come a very long way in two generations. Let's hope that the next 60 years see China's growth into a model citizen and stalwart supporter of the international system — for its own sake and for ours.

Nina Hachigian, a senior fellow at the Center for American Progress, is the co-author of "The Next American Century: How the U.S. Can Thrive as Other Powers Rise." She wrote this commentary for the Los Angeles Times.