The survey by YouGov (pdf), shown exclusively to the Guardian, has the secretary of state beating Romney by 51% to 45% among likely voters. Obama leads Romney by 48% to 47%.
YouGov estimates that Clinton's lead would translate into a massive victory in the electoral college, by 347 to 191 votes. The polling company, which surveys regularly in the US, believes Clinton would win both Florida and North Carolina, states that it projects Obama to lose.
The findings are likely to add to the clamour for Clinton to seek the presidency in 2016, when she would be the frontrunner for her party's nomination.
Many Obama supporters will not be too rattled by the survey. For one thing, hypothetical candidates tend to do better than actual ones, especially incumbents. Obama is saddled by the baggage of four years in the White House; Clinton is relatively untarnished by comparison.
Secretaries of state are often more popular than the presidents they serve, as both Colin Powell and Condoleezza Rice discovered. They enjoy the prestige of high office but have to make no unpopular domestic decisions and bear no responsibility or blame for the economy.
Still, the poll shows Clinton performing more strongly than Obama among almost every group: men and women, Republicans and independents, those earning less than $40,000 a year and those earning more. Among white voters the president trails Romney by 21 points; Clinton would cut that advantage to 14 points.
Only among African Americans does Clinton enjoy less support than Obama: she would beat Romney among black voters by 89% to 10%, while Obama beats the Republican even more thoroughly, by 91% to 5%.
"The key thing is that Hillary can reach certain white demographics far better than Obama, and this is only partly offset by Obama's appeal among black voters," said YouGov's president, Peter Kellner.
That finding revives a claim made often during the 2008 primary contest between Obama and Clinton, when the former first lady enjoyed an advantage with white, low-income Democratic voters in blue-collar states where Obama struggled.
Longtime Clinton supporters will be delighted at the remarkable distance the former first lady has travelled in the 20 years since her husband was first elected to the White House. Back then she was a polarising figure; a 1990s bumper sticker declared "Life's a Hillary". Now she may well be the most popular politician in the US.
• YouGov questioned a representative sample of 1,000 US adults online between 27-29 October. The sample was stratified by age, gender, race, education, and region. The raw data was then weighted to match the profile of registered voters by age, gender, race, education, news interest and ideology.
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