TAMPA, Fla. — On the eve of their national party conventions, President Obama and Mitt Romney are locked in a close race to amass the requisite 270 Electoral College votes for victory. The contest is where it was at the start of the long, volatile summer: focused on seven states that are up for grabs.

Neither candidate has a significant advantage in Colorado, Florida, Iowa, Ohio, Nevada, New Hampshire and Virginia, which offer a combined 85 electoral votes, according to an analysis of public and private polls, spending on television advertising and numerous interviews with Republican and Democratic strategists in those battleground states.

The analysis, which also took into account the strength of a candidate's on-the-ground organization and travel schedules, found that if the election were held today, Obama would have 19 states and the District of Columbia, offering 247 votes, solidly in his column or leaning his way, while Republican Romney would have 24 states with 206 votes.

Obama won all seven of the too-close-to-call states in 2008, and they are where the race will primarily be contested in the homestretch to the Nov. 6 election.

Romney also is considering trying to expand the battleground map in the coming weeks, watching for an opportunity to compete more aggressively in Wisconsin, and possibly Michigan and Pennsylvania. Republican-leaning groups have been running ads in those states to lay the groundwork for Romney.

Ten weeks before Election Day, the analysis isn't meant to be predictive but rather is intended to provide a snapshot of a race that has been close all year.

Among the unknowns that could shake up the electoral landscape before November: the latest unemployment figures that come out next month; an unexpected foreign-policy crisis in Syria or Iran; and the outcome of the candidates' October debates.

Both sides are working to win over the 23 percent of registered voters who said in an Associated Press-GfK poll that they are either undecided about the presidential race or iffy in their support for a candidate.

To woo them, the campaigns and political parties, along with allied groups with access to unlimited financial contributions, have spent $540 million on television advertising, according to ad-spending reports. And there are a lot more ads to come.

The national party conventions, starting with Republicans in Tampa on Monday and ending with Democrats the week after in Charlotte, N.C., will set the parameters of the fall campaign, and could provide each side with at least a temporary surge of support in national polls.