The United States will likely be the "first among equals" in 2030 in an increasingly chaotic world where China is the top economy and demand soars for resources, a US intelligence report said Monday.

The National Intelligence Council, in its first assessment in four years aimed at shaping US strategic thinking, said that China will surpass the United States as the largest economy in the 2020s, in line with independent forecasts.

But the study said that the United States, while weaker, will probably remain the top player in two decades thanks to its role in resolving global crises, its technological prowess and its "soft power" that attracts outsiders.

"The US most likely will remain 'first among equals' among the other great powers in 2030 because of its preeminence across a range of power dimensions and legacies of its leadership role," the 137-page report said.

"Nevertheless, with the rapid rise of other countries, the 'unipolar moment' is over and Pax Americana -- the era of American ascendancy in international politics that began in 1945 -- is fast winding down," it said.

The study predicted that Asia's economy, military spending and technological investment would surpass those of North America and Europe combined by 2030, but warned of major uncertainty over an emerging China.

"If Beijing fails to transition to a more sustainable, innovation-based economic model, it will remain a top-tier player in Asia, but the influence surrounding what has been a remarkable ascendance will dissipate," it said.

China's global power is likely to keep rising but at a slower rate -- a phenomenon of easing growth that, according to historical precedent, makes countries "likely to become fearful and more assertive," the study said.

If tensions keep rising in Asia, more nations will embrace US leadership and China "can be its own worst enemy," the report's lead author Mathew Burrows told reporters.

Europe, Japan and Russia are expected to maintain slow economic declines through 2030, while a number of middle-tier countries could rise, such as Colombia, Egypt, Indonesia, Iran, Mexico, South Africa and Turkey, it said.

The study expected major benefits from technology by 2030, but warned that climate change threatened to pose serious challenges.

With a growing population and rising incomes, the planet's demand for water, food and energy will grow by 35, 40 and 50 percent respectively by 2030, it said.

A wealthier China and India would likely need to rely more on food imports, driving up international prices. Families in low-income nations would feel the pinch hardest on food, likely fueling social discontent.

The National Intelligence Council estimated that the world will have nearly 8.3 billion people in 2030, up from 7.1 billion now, but that the average age will be older -- with potentially giant consequences.

The study said that 80 percent of armed and ethnic conflicts occurred in nations with youthful populations. The number of youthful states will fall significantly by 2030, with the bulk of the remaining ones in Africa.

Other areas that will still have youthful populations -- and the fuel for potential conflict -- include Afghanistan, western and tribal areas of Pakistan and India's poorer northern states of Bihar and Uttar Pradesh, it said.

By contrast, the study found that the Middle East "will be a very different place" in 2030 with the gradual aging of the youth bulge that took to the streets in the Arab Spring protests that brought down autocratic leaders.

But the report predicted instability in nations with rooted sectarian or other tensions such as Bahrain, Iraq, Libya and Syria along with Yemen, which the study predicted could break up for the second time.

The study doubted that Al-Qaeda would pose a threat in 2030, saying that terrorism by its nature alienates initial supporters.

"By 2030, we believe that the Islamic terrorism cycle may have exhausted itself," Burrows said.

Iran was a question mark. The study expected "far-reaching instability" if Iran developed a nuclear weapon, but also said that a more pro-Western Iran could emerge due to public pressure and infighting within the clerical regime.

The study said a potential resolution to the Israeli-Palestinian conflict would have "dramatic consequences," but suggested that a more likely scenario consisted of unofficial actions that lead toward a Palestinian state with key issues such as the status of Jerusalem remaining unresolved in 2030.