Combined, these states offer 68 of the 270 electoral votes needed for victory on Election Day, Nov. 4.
Pollsters attributed Obama's improved standing to the public's general approval of his debate performance, antipathy toward GOP vice presidential nominee Sarah Palin and heightened confidence in the Illinois senator's ability to handle the economic crisis.
The fresh polling is the latest troublesome turn for McCain, the Arizona senator who is trying to regain control of the campaign conversation amid increasingly difficult circumstances for Republicans. It comes on the eve of a debate between Palin and her Democratic counterpart, Joe Biden, and as the financial crisis shapes the presidential race in unpredictable ways.
For now and probably for the next month, the race will be entirely about who can best handle an economy in peril.
The war in Iraq, national security and foreign policy issues - McCain's strengths - have largely fallen by the wayside as each campaign tries to chart a course to the presidency in extraordinarily choppy economic waters.
The new surveys show Obama leading McCain in Florida 51 percent to 43 percent, in Ohio 50 percent to 42 percent and in Pennsylvania 54 percent to 39 percent.
Since 1960, no president has been elected without winning two of those three states.
The results are notable because they show Obama in a strong position in the pair of states that put Bush in the White House in 2000 and kept him there four years later - Florida and Ohio, with 27 and 20 electoral votes, respectively.
Obama has been struggling to break into a comfortable lead in both states; for weeks he had been mostly about even with McCain in Ohio while lagging for months in Florida, even after being the only candidate on the air and spending some $8 million on advertising.
Pennsylvania, with 21 electoral votes, is a different story.
Obama is trying to hang onto the state Democrat John Kerry won four years ago, though McCain has mounted a stiff challenge as he seeks to benefit from his rival's trouble with working-class voters who question his liberal voting record and, perhaps, his race.
The telephone polls, which were taken before and after last week's McCain-Obama debate, have margins of error ranging from plus or minus 2.8 percentage points to plus or minus 3.4 points.
On the Net:
Quinnipiac Poll: http://www.quinnipiac.edu/polling.xml