WASHINGTON (CNN) -- A wide-open presidential race and a willingness by candidates, interest groups, unions and corporations to buy TV time will lead to historic spending for political and issue-advocacy advertising in the 2008 election cycle, an analysis shows.

Former Massachusetts Gov. Mitt Romney has spent the most on TV advertising so far among presidential contenders.

The cost to try to influence the 2008 election could exceed $3 billion, according to TNS Media Intelligence/Campaign Media Analysis Group, CNN's consultant on political television advertising.

This is nearly twice as much than what was spent in 2004 when political and issue-advocacy television advertising rang in at $1.7 billion. In 2006, $2.3 billion was spent on political and issue-advocacy TV commercials.

Just about every candidate running for an office from dogcatcher to president is spending the money, said Evan Tracey, CMAG's chief operating officer.

The costs to produce a TV commercial are no longer prohibitive for local and state candidates, who are turning more and more to the airwaves to reach voters.  See how spending breaks down for this year »

And interest groups have spent $6.2 million on TV ads so far this year for state and local ballot measures.

On the national level, the cost of issue-advocacy television ad spending was $270 million in the first nine months of this year. Subjects ranged from the Iraq war to telecommunications reform. Television ads on health care alone total $60 million.

CMAG estimates more than $3 million of the $270 million spent to air issue-advocacy ads this year has gone for commercials in states and districts that are likely to have competitive House and Senate races in 2008.

Tracey said he thinks this is just the beginning of interest groups "pivoting from legislative advocacy mode to political mode."

"What we expect to see between now and the end of the primaries, and through the general election, is groups will take a more aggressive stance on their advertising and actually target candidates," he said.

With 17 Democratic and Republican candidates running for president, CMAG predicts that more than $800 million will be spent on TV ads in the battle for the White House.

Up to now, the political commercials have been largely focused on the early states of Iowa, New Hampshire and South Carolina. Voters in some of the 20-plus states holding nominating contests on February 5 will start seeing ads in the coming months.

Former Massachusetts Gov. Mitt Romney leads all candidates in TV spending, having aired his commercials more than 11,000 times this year at a cost of nearly $8.6 million. This is a record for the number of airings at this point in a presidential election cycle.  Watch how Romney is way ahead in ad spending »

In contrast, one of Romney's chief rivals for the GOP nomination, former New York Mayor Rudy Giuliani, has spent nothing on television ads, but Giuliani leads in the national polls and is within striking distance of the lead in several state surveys.

Giuliani enjoys widespread national name recognition, while Romney does not.

In the race for the Democratic nomination, Illinois Sen. Barack Obama has spent more than $2.3 million on television commercials, while New York Sen. Hillary Clinton has spent $1 million less and leads in both national and early state polls.

New Mexico Gov. Bill Richardson has probably benefited the most in the Democratic contest from the $2 million he has invested in his television commercials.

Richardson's humorous TV ads effectively stated his experience as a lawmaker, diplomat and executive, and positioned him as a solid second-tier candidate.

Romney used his $8.6 million in television ads to introduce himself as a social and fiscal conservative to Republican voters. These voters might otherwise not know much about him other than that he was the governor of the traditionally liberal Massachusetts.

Romney is leading polls in the early voting states of Iowa and New Hampshire.

Further evidence of how Romney's television commercials have helped is in South Carolina.

An American Research Group poll of South Carolina Republicans in August showed Romney registering at 9 percent with
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