The poll of 2003 people found 53 per cent believe "the US plays a less important and powerful role as a world leader than it did a decade ago".
The percentage saying this has jumped 12 points since 2009 and has more than doubled since 2004, when it was 20 per cent. Is this another brick in the wall in the much debated scenario where China trumps America? Or, in another version, has US power peaked as Britain's did a century ago?
Maybe. But the poll reflects American perceptions amid war weariness following conflicts in Iraq and Afghanistan - isolationist sentiment surfaced after the Vietnam War - and a recession that have dented national confidence.
"It's not an objective measure of US power," says senior Pew centre researcher Juliana Menasce Horowitz.
"So to say the US is less powerful than it was doesn't mean that by objective measures this is true. The poll showed 48 per cent believe China is the world's top economic power. But that's not true."
For while Americans are reluctant to engage in another "nation building" war - US opinion sharply opposed fighting Syria - the poll shows a preference for shared leadership, favoured by 72 per cent.
"There's quite strong support for remaining engaged with the world through trade deals and alliances," says Thomas Wright, a fellow at the Brookings Institute.
So what does the poll tell US policy makers, especially possible presidential candidates as they mull the post-Obama era and the 2016 election?
"The results send a mixed message," writes James Lindsay, a senior vice-president at the Council on Foreign Relations - a non-partisan foreign affairs think tank.
"Americans are reluctant to embrace world leadership, but they are also reluctant to abandon it."
He noted Americans were "sceptical Washington is striking the right balance between domestic and foreign policy", but cautioned against a rush to "Fortress America" assumptions.
The challenge is how to reconcile the two in a global economy as rivals seek to expand their influence, an impulse fraught with the possibility of conflict.
The poll shows many Americans feel deep unease about life at home.
Protecting jobs was the second highest priority - protecting the US from terrorists was the first - as hard times and labour unrest focus minds on economic inequalities.
David Simon, whose Wire television series tracked how drugs fuel a parallel economy in an American city, says there are two nations. One shares in the dream, the other does not. Obama has called the growing disparity between America's rich and poor "the challenge of our time".
In an important caveat, 77 per cent believe trade and business ties are good and want the US to be involved in the world economy.
Despite hardship at home, this view has jumped 24 percentage points since the US recession started.
Conducted before the interim deal on Tehran's nuclear programme, the poll assesses a tempestuous year for President Barack Obama's foreign policy, as the US adjusts to an emerging multi-polar world that challenges its superpower hegemony.
Buffeted by his failure to rally support for air strikes on Syria, the President faced criticism of US drone strikes, fallout from National Security Agency whistleblower Eric Snowden's revelations about US spying, and strained relations with China, Russia and Latin America.
The poll gives him poor foreign policy ratings, mostly below 40 per cent, although he scores 51 per cent for tackling terrorism and 50 per cent support for drone strikes.
Syria was a magnet for criticism, with 72 per cent of CFR respondents saying Obama's performance weakened US prestige and enhanced Russia's. Fifty-one per cent said he was "not tough enough" in foreign policy and national security issues.
Seventy per cent considered the US to be less respected today than before, compared to 71 per cent in 2008.
In a nation where a deep sense of exceptionalism reinforces a sense of entitlement - a duality played up repeatedly by US leaders - this is a sobering reality check.
Has the American Century peaked? Has the public sensed a change, perhaps pivotal? Measuring US decline against China's rise - arguably a return to centuries of historical normalcy - has become a geopolitical cliche. But it is premature to dismiss the US and anoint China.
Even broke and battered the US remains a dynamic and innovative nation, adept at projecting hard or soft power to protect and expand its interests.
Crises demand Washington's response; can the US remain aloof from Moscow's bid to strong-arm the Ukraine into its orbit? Can it defuse Japanese-Sino tensions in the East China Sea?
Geopolitics are hard to predict. A century ago two titans, Britain and Germany, vied for power. War cut them both down and by mid-century the US was the West's sole superpower. China may be back, but the US has yet to leave the building.
In the aftermath of Typhoon Haiyan it was US military might, in the shape of an aircraft carrier, that demonstrated Washington's long reach. China, one of Manila's Asian neighbours, lingered on the sidelines, perhaps unable to rise above a territorial dispute with the Philippines.
As both nations scramble for influence in Africa, the Chinese leader Xi Jinping sent his deputy to Mandela's funeral. Obama gave the rapturous crowd one of his keynote speeches (he delivered another in Cairo in 2009), signalling US interest in the continent as it strides on to the global stage.
Africa's potential may sharpen Sino-US competition but climate change, poverty, refugees and other global concerns demand a concerted response.
"A lot of these problems are transnational and can only be solved by co-operating with other countries," says Wright. "In a multipolar world people recognise it's important to work with other nations and to have partnerships."
Last year, another Pew poll found American exceptionalism had declined, from around 60 to 50 per cent over the past decade.
As America ponders how to project leadership in a changing world, humility may prove a valuable asset.
