NEW YORK – Now the campaign ad crush and TV spending spree really begins in the presidential race.

The TV ad campaign, with total spending expected to swell to $1.1 billion, starts up again now that the party conventions are over and the sprint to the general election is under way.

Just over one-third of that amount has been spent so far, according to the Kantar/Campaign Media Analysis Group, which tracks campaign ad spending. That means the campaigns and independent groups will spend more on the air in the final eight weeks of the presidential contest than they did in the first five months.

The biggest change is on the Republican side, with Mitt Romney now free to tap millions in general election funds he had collected but could not spend until becoming the party’s official nominee. That means the GOP’s significant spending advantage over President Obama and his Democratic allies will grow, making it the first time that an incumbent will have been outspent on the air.

National polls show Obama and Romney in a virtual dead heat, but only eight states are considered true battlegrounds: Colorado, Florida, Iowa, Nevada, New Hampshire, North Carolina, Ohio, and Virginia. Obama carried them all in 2008, but they are too close to call for now.

Flush with new cash, the Romney campaign poured nearly $5 million into ads in those states beginning this weekend. A series of state-specific ads hit Obama on defense spending, business regulations and housing.

Republican-leaning independent groups led by the American Crossroads and Crossroads GPS kept Romney in the game throughout the summer while he regrouped from a tough primary contest. Priorities USA Action, the only significant pro-Obama super PAC, has been far outpaced by the conservative-leaning groups.

Those and other independent groups emerged after a 2010 Supreme Court decision loosened campaign finance laws, allowing wealthy individuals to spend unlimited sums on political activity as long as they stay separate from the campaigns themselves. The Crossroads groups are backed by former President George W. Bush’s longtime political counselor Karl Rove. Americans for Prosperity, another pro-Romney group, was founded by the billionaire brothers Charles and David Koch.

Together, the Crossroads groups spent about $66 million on ads through the end of August. Of that, $58 million came from Crossroads GPS, which is organized as a social welfare group under tax laws and thus does not have to disclose its donors. AFP, which also does not disclose its donors, spent $35.2 million during that time.

The Obama campaign spent $166 million on ads through Aug. 30, compared with $74 million by the Romney campaign and $22 million by the Republican National Committee. But now, with Romney’s general election resources available and the Republican-leaning groups continuing to air ads, the Obama campaign seems set to be swamped on TV.