As the final days before the Democrats’ Iowa caucuses and New Hampshire primary wind down, you can expect all of the credible hopefuls to be on television with a cacophony of political ads in which they extol their own virtues and slam their opponents. [IMGCAP(1)]

Massachusetts Sen. John Kerry launched a television advertising barrage in Iowa and New Hampshire in late December in the hope of boosting his flagging campaign, and Connecticut Sen. Joe Lieberman has had a series of conference calls with members of the media to hype his new TV spots in New Hampshire.

But if you could inject truth serum into the veins of the consultants directing the campaigns of the top-tier hopefuls, they would each tell you the same shocking thing: TV ads are hugely overrated as electoral weapons.

One of the great ironies of politics is that the higher the office being sought, the less important television spots are in determining the winner. That’s right — LESS important, as long as all candidates have roughly the same number of gross ratings points up on the air. (Quite obviously, if one candidate is running thousands of points of ads and another isn’t running any spots, the ads are more likely to sway voters.)

Television ads are very important in races for the House, since House candidates and campaigns receive little “free media” coverage in newspapers and on television. The ads give voters information they otherwise wouldn’t have.

But paid ads are less important in Senate contests and of relatively little importance in the presidential race. Newspapers, news magazines and the electronic media give considerable coverage to competitive, high-profile statewide contests, providing voters with information generally viewed as more reliable than paid, self-serving television advertisements.

Voters use debate coverage, in-depth media reports on the candidates and their positions on the issues, and news coverage of the back-and-forth arguments of the campaign to form opinions about the candidates. Most paid TV ads, particularly those in the campaign’s final weeks, are so predictable and obvious in their purposes that voters tend to discount them.

It’s only the rare TV ad — maybe the so-called Willie Horton spot, or the shot of Michael Dukakis sitting in a tank — that really moves numbers in a presidential contest.

Television ads tend to be more important in presidential primaries than in the general election (since most voters pay more attention to the general election than to most primaries), but they are notably less important in Iowa and New Hampshire than in virtually any other primary or caucus state in the country.

Voters in those two states have become accustomed to seeing and listening to presidential hopefuls in the flesh. Candidates spend a lot of time in both states, and the print and electronic media in each give heavy coverage to the nation’s first caucus and first primary.

“The electorate in Iowa and New Hampshire is extremely spoiled. They want you to have lunch with them,” says GOP consultant Curt Anderson, who was active in businessman Steve Forbes’ 2000 GOP presidential effort.

“Paid media will keep you on the playing field, but it will not win the game for you. Only organization will win it for you,” veteran Democratic campaign strategist Donnie Fowler told me recently.

Some of the late TV ads have been particularly vacuous.

One Kerry spot has the Senator telling voters that it’s time to make energy independence “a national priority,” and asserts that the nation should never have to go to war for oil. Wow, that’s a novel idea. When voters in the two early states hear that, I’m sure they are going to stampede to the Massachusetts Senator.

Not only is energy independence not a new idea, but Kerry doesn’t have a monopoly on it. Every Democrat has talked about it, so it’s difficult to see how the Massachusetts Senator can change the dynamic of the Democratic race with the issue.

If late TV spots in Iowa or New Hampshire are going to have an effect, they are going to have to provide Democratic voters with new information. The same sort of generic messages that we’ve seen for months won’t work unless a candidate is overwhelming his opponents by outbuying them.

Changes in the way spending is calculated against each state’s “spending cap” ensured that Democratic contenders in Iowa would spend more on television than did presidential hopefuls in the past. And yes, some late deciders will be moved by a late ad or two. But after weeks — or in some cases months — of heavy “earned media coverage,” new TV spots in Iowa and New Hampshire aren’t likely to sway many Democrats.

Stuart Rothenberg is editor of the Rothenberg Political Report.