Former Massachusetts Gov. Mitt Romney is leading the growing pack of Republican presidential candidates and is the only one neck-and-neck with the sitting president, according to a new poll released Tuesday.

The Washington Post-ABC poll suggests that widespread concerns about the state of the economy continue to make President Obama vulnerable, despite questions about the quality of the GOP field. The survey shows that Romney, who formally launched his economy-focused campaign last week, is starting off strong.

The poll showed Obama leading five other potential rivals but in a dead heat with Romney, each with 47 percent among all Americans. But among registered voters only, the poll put Romney ahead, 49 percent to 46 percent.

About six in 10 of those surveyed gave the president negative ratings on the economy and deficit.

The poll also revealed lingering problems for former Alaska Gov. Sarah Palin, who stirred speculation about a possible run when she launched a bus tour of historic sites more than a week ago. The poll showed Palin trailing slightly behind Romney among Republicans and Republican-leaning independents in a primary. But 42 percent of Republicans said they've ruled her out, and almost two-thirds of all those surveyed said they would "definitely" not vote for her. In a general election against Obama, she fared worst of all six candidates tested in the poll.

The other four candidates tested against Obama were former House Speaker Newt Gingrich, former Utah Gov. Jon Huntsman, former Minnesota Gov. Tim Pawlenty and Rep. Michele Bachmann, R-Minn. Of them, only Gingrich and Pawlenty have formally announced a bid.

Though some speculated that Palin stepped on Romney's toes last week by arriving in New Hampshire as Romney announced his White House bid, Romney told CNN Monday that she actually did him a favor by stealing some of the spotlight, calling his greatest enemy "overexposure."

The poll of 1,002 adults was conducted June 2-5. It had a margin of error of 3.5 percentage points.