WASHINGTON - Four months ahead of the US presidential election, sitting President Barack Obama retains a narrow lead over Republican presumptive nominee Mitt Romney in key swing states, according to a new poll released on Wednesday.

The new poll, conducted by NBC and Wall Street Journal found that Obama led Romney by 50 percent to 42 percent among 12 swing states, which are viewed as battlegrounds for the November election, including Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, New Mexico, North Carolina, Ohio, Pennsylvania, Virginia, and Wisconsin.

According to the latest survey, Romney's favorable score is 30 percent in the swing states, down from the previous month's 36 percent.

The survey concluded Romney's favorability numbers have dropped in those swing states, possibly reflecting the toll the negative Obama TV advertisements are having on the former Massachusetts governor in these battlegrounds.

About 33 percent of swing state residents said they had a more negative opinion of Romney based on what they had seen, read or heard about his business record recently.

The poll also shows that attitudes about Romney's business background, a frequent target in Obama ads, are more unfavorable in these battlegrounds.

The survey also found that race between the incumbent and the challenger is almost unchanged in the nation-wide range, following the past month occupied by debates over the disappointing May jobs- creation numbers, the economic uncertainty in the eurozone crisis, the Obama administration's recent immigration shift, and the Supreme Court's decision on health care overhaul to be released on Thursday.

Obama and Romney were still locked in dead heat nationwide, said the poll. Obama won 47 percent supporters and Romney won 44 percent, which was within the margin of error.