U.S. Republican presidential nominee Mitt Romney leads President Barack Obama by four percentage points among likely voters in top swing states, thanks to a surge in support by women voters, finds a latest poll on Tuesday.

As the two candidates heading into the second debate Tuesday night in New York, the USA Today/Gallup Poll shows that Romney is leading Obama 50 percent to 46 percent in 12 crucial swing states, as Obama's previous lead among women voters has sharply declined to a virtual tie of 49 percent to 48 percent.

Nationwide, Gallup finds the candidates are locked in a dead heat. While Obama enjoys a slight lead over Romney among registered voter by 48 percent to 46 percent, Romney leads Obama among likely voters by 49 percent to 47 percent.

Women voter are crucial for a victory for Obama as he led former Republican challenger John McCain by 13 points among women voters in the 2008 presidential race.

Before the first debate held on Oct. 3, in which Obama had a passive and lackluster performance, the incumbent had enjoyed a wide lead among women voters over Romney, the former Massachusetts governor and successful businessmen who was widely regarded as out of touch with common citizens.

"In every poll, we've seen a major surge among women in favorability for Romney" since his strong performance in the first debate, Democratic pollster Celinda Lake was quoted by the USA Today as saying.

After the debate, women voters apparently changed their mind about Romney, thinking he "might understand their lives and might be able to get something done for them," Lake added.

Among likely male voters in the swing states, Romney leads Obama by 52 percent to 44 percent, the poll finds. The swing states include Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, New Mexico, North Carolina, Ohio, Pennsylvania, Virginia and Wisconsin.

Eager to contain the rapid rise in voters support for Romney less than a month before the Nov. 6 Election Day, Obama is expected to adopt a more aggressive style in the second debate to be held at the Hofstra University in New York.

The debate, the last of its kind, will be held in a town-hall format, in which both candidates will answer questions from undecided voters on their policies on domestic and international issues.