Much has been made this year of the presidential candidates' increasingly sophisticated online "conversations" with voters. But when it comes to Americans' favorite tool for navigating the web, it turns out most White House contenders are still pretty clueless, a recent round of experiments on Google's AdWords program suggests.

The experiments conclude that most of the presidential candidates are sitting on the sidelines as American voters search for timely information about political issues or campaign events.

The exceptions include Arizona Sen. John McCain and former Massachusetts Gov. Mitt Romney, who use Google's AdWords keyword bidding program around searches for issues and news events. On the Democratic side, Illinois Sen. Barack Obama appears to be the only one using AdWords in the same fashion, though Edwards has purchased keywords in the past.

Just over half of all search activities on the web in the United States – 3.9 billion queries – took place on Google, according to June data from Nielsen/NetRatings. Yahoo's search accounts for 20 percent, and 13 percent of web surfers use MSN/Windows Live Search. Seven other search engines share the remainder of the market.

During the Ames Straw poll last Saturday, Romney appeared in the top paid results in searches for variations of the keywords "Iowa straw poll results," which was the most searched for term that day on Google, according to the Google Trends experimental search trends tracking tool.

A search on any day on the phrase "war in Iraq," (a policy item that tops voters' agenda, according to The Gallup Poll) also yields Romney's website as a top paid search result. That's a savvy move for the campaign, given that Romney scores the lowest among the leading presidential contenders in a recent Gallup poll on candidates' ability to handle the war in Iraq. Gallup notes that the reason for the low score is related to the fact that a fifth of Americans don't have an opinion on how Romney would handle the issue.

And a search for the phrase "presidential debates" on Google on Wednesday morning yielded McCain's campaign website as a paid search result. On Tuesday morning, Obama's campaign site also appeared; the ad exhorted readers to volunteer at Obama events.

The candidates are missing a prime opportunity to capitalize on surges of interest online generated by news events, such as televised debates and other television appearances, says Richard Ball, founder of Apogee Web Consulting, a search-engine marketing firm based in the Baltimore, Maryland, area. Ball recently conducted experiments on Google's AdWords program with "Iowa straw poll results," on Saturday, and with various versions of the phrase "you tube debate," and "democratic debate" in July.

"I couldn't believe the (Democratic) candidates weren't doing such a simple thing as buying keywords," Ball said in an interview.

Ball said that he is particularly surprised because he considers AdWords advertising unusually cost-effective – candidates don't have to pay when their ad appears on Google, only when users click through to their sites. And in his Saturday experiment, the cost per click for reaching voters was 13 cents.

"For less than the cost of postage, a presidential candidate could have acquired a visitor to their election campaign website," Ball wrote on his blog. "How much would a direct-mail advertising campaign have cost to acquire 1,820 visitors to their site? How much would a radio or TV or print-ad campaign have cost to generate that much interest?"

Indeed, this is precisely why the McCain campaign uses AdWords so extensively, says Eric Frenchman, chief internet strategist at the political marketing agency Connell Donatelli in Washington, D.C. The firm handles all of McCain's online advertising.

Frenchman estimates that the McCain campaign receives $4 back for every dollar spent on Google's Adwords program. The McCain campaign has been using AdWords since the beginning of the campaign.

"I really think (campaigns should advertise) around issues," Frenchman says. "It's simple for people to go around buying candidates' names, but people are looking at gas prices and the war in Iraq."

"If candidates have a strong view on the subjects, then they need to get that across – I don't think people are taking enough of a look at that," he adds.

An online survey released in July confirms Frenchman's hypothesis. ICrossing, a Scottsdale, Arizona-based digital marketing company, used 129 issue-keyword phrases to test the candidates' advertising across Google, Yahoo and MSN. The study found that very few of the candidates' names popped up when those phrases were used as search queries.

Peter Greenberger, manager of Google's elections and advocacy team of four, also confirms this, but predicts it will quickly change.

"What I haven't seen is campaigns integrating their AdWord buys with real-time news events, initiatives and promotions," Greenberger says.

"If you're running a television ad in Iowa, or you've said something clever in a debate you want to re-state, or what a (rival candidate said) you could do a rapid response text or image ad, and I think that's what we'll see as we head into the Fall campaign season."