With few voters still on the fence, President Barack Obama holds leads over Mitt Romney in new polls of Ohio, Florida and Virginia, three of the states likely to determine who wins the White House in November.

Mr. Obama has fought Mr. Romney to a draw on the question of which candidate is best equipped to grapple with the economy, the new Wall Street Journal/NBC News/Marist Poll surveys suggest. Mr. Romney's campaign is built largely on an argument that he can best reinvigorate...