Attorney General Rob McKenna, the likely Republican nominee for governor, is crushing his Democratic rival, Jay Inslee, by at least one measure: online advertising. McKenna, according to campaign-finance records, has outspent Inslee online by a factor of nearly 34 to 1.

While the two campaigns have raised similar amounts of money, the McKenna campaign has spent $103,619 on online advertising during the past 13 months, records compiled by the Public Disclosure Commission indicate.

The Inslee campaign has spent $3,070 — less than a third of the $10,417 McKenna spent on Facebook ads alone.

The Inslee campaign didn't seem troubled by the advertising imbalance. Sterling Clifford, Inslee's communications director, emphasized the campaign's "organic" outreach through social-media outlets like Facebook and Twitter, which do not eat up the campaign's advertising budget. (About 3,910 people followed @JayInslee on Twitter as of last week; 2,811 followed @robmckenna.)

"We have not felt compelled to spend money to draw people in," Clifford said.

But high engagement on social media isn't a substitute for an effective online ad campaign, said Darrell West, director of the Center for Technology Innovation at the Brookings Institution, a Washington, D.C., think tank, who has researched political advertising.

Sites like Facebook — on which Inslee had 17,865 "likes" last week compared to McKenna's 28,371 — can get people talking about a candidate, West said, but don't allow for much control over what's being said about him or her. "With online advertising, you have direct control over the message being communicated," he said.

McKenna's investment in online ads echoes a national trend toward more digital campaigns. Though television remains the chief advertising medium for campaigns, West said, President Obama and his presumptive Republican challenger Mitt Romney have each devoted about 10 percent of their ad budgets to the Internet this election.

"I think this will be the first truly digital election, in terms of online advertising," he said.

Little research into online advertising exists, said Aaron Smith, a senior research specialist with the Pew Internet & American Life Project, which studies how people use the Internet. But Smith has studied Americans' use of the Web for campaign news, which has shot up in the past few years. "I would suspect the same is true with advertising as well, although we haven't researched it directly," he said.

According to Pew, 54 percent of American adults went online to get political information during the 2010 midterm elections. Nearly a quarter of adults cited the Internet as their main source of campaign news, up from 15 percent in 2006. Still, two-thirds of Americans got most of their news from television in 2010.

But online advertising offers some advantages TV does not.

"The beauty of online advertising is that you can target so well," said Charles McCray, McKenna's communications director.

During McKenna's first debate with Inslee in Spokane in June, for instance, the McKenna campaign advertised with The Spokesman-Review newspaper.

Twenty years ago, the campaign might have simply bought an ad in the paper. But with online advertising, McCray said, they were able to "select the page we think folks are most interested in hearing from Rob McKenna on" — the one with the article about the debate on the paper's website.

That makes online advertising an effective way to spend a limited number of advertising dollars, McCray said. (The McKenna and Inslee campaigns have raised roughly equal amounts of money to date — about $6.7 million each, according to the Public Disclosure Commission.)

The nation's big political-advertising agencies are getting the message. McKenna's campaign has spent most of its online ad budget with Arena Communications, a prominent direct-mail firm based in Salt Lake City that also began offering online advertising services in 2010. "If you're a campaign and you're just spending money on traditional media — and I'd say that's phone, TV and mail — you miss people," said Ben Olson, who works on Arena's digital staff.

While Obama helped pioneer the Internet campaign in 2008, there isn't much of a difference in how Democrats and Republicans use the Internet, according to Smith, the Pew researcher. In this race, the Republican candidate is outspending the Democratic one online.

McKenna and Inslee, a former U.S. congressman, have been tied for public support in recent polls.

"That they've spent more money to achieve a similar result doesn't concern me," Clifford said.

The Inslee campaign has spent its online advertising budget with one company, Trilogy Interactive in Palo Alto, Calif., which has purchased ads through Facebook, Yahoo and Google.

McKenna's campaign initially divided its ad budget between Facebook and Emotive, an online advertising agency based in Arlington, Va. The campaign spent $30,626 with the two companies over the first 10 months of the race, according to Public Disclosure Commission records.

In March, McKenna switched to Arena, which has worked with a number of well-known Republicans, including Senate Minority Leader Mitch McConnell, of Kentucky and U.S. Rep. Michele Bachmann, of Minnesota. He has spent $72,993 with Arena in the past four months.

Those numbers are likely to be dwarfed by the amount the campaigns spend when they start buying ads on TV. The Inslee campaign rolled out its first commercial this week.

McKenna hasn't aired any TV commercials to date, but the Republican Governors Association has reserved $1.9 million worth of television time in Washington for the fall campaign.

Yet, the TV commercials may not reach many people in their 20s, who are watching less TV and spending more and more time on the Web. That's where the online ads come in, McCray said.

"That's where, for some folks, this election will play out," he said. "On a computer monitor."

Theodoric Meyer: 206-464-2985 or tmeyer@seattletimes.com. Twitter: @theodoricmeyer.