Is John McCain preparing to pull off a surprise to slow Barack Obama’s post-convention bounce by naming a low profile former congressman-turned Washington lobbyist who worked in both Bush White Houses as his running mate?

That’s what some McCain advisers and GOP insiders think might happen as they discussed the possibility Thursday that McCain could confound the political experts by choosing former Ohio Rep. Rob Portman as the GOP vice presidential candidate.

Speculation that Portman may be McCain’s choice was sparked by the news that the Arizona senator will appear with his running mate Friday at a campaign stop in Dayton. Ohio, a must-win state for McCain, as he heads for next week’s Republican National Convention in St. Paul.

“I know for a fact that Portman is in the running,” a Republican lawyer with close ties to McCain told me Thursday.

While Portman, who spent a dozen years in Congress before heading the Office of Legislative Affairs for the first President George Bush and serving as U.S. Trade Representative and White House budget director for the second, isn’t among those most frequently named as McCain’s likely choice, he would bring considerable strength to the ticket.

Portman, now a partner in a Washington law firm, could boost McCain’s election prospects in several ways. At 52, he’s 20 years younger than McCain, and his quiet manner and button-down style could serve to soften McCain’s combative and sarcastic manner.

More importantly, Portman has tons of expertise in an area where McCain, by his own admission, is weakest, on economic policy.

His work on foreign trade also boosts his diplomatic credentials and ability to deal with NAFTA and other issues of a globalized economy, while his conservative record on social issues would appeal to a party base that can’t stand former Massachusetts Gov. Mitt Romney and isn’t crazy about former Pennsylvania governor and Homeland Security Secretary Tom Ridge, two of the names on McCain’s VP short list, along with Minnesota Gov. Tim Pawlenty and Democrat-turned-Independent Sen. Joe Lieberman

Finally, Portman would more than hold his own in debating Barack Obama’s golden-tongued running mate, Sen. Joe Biden, after standing in for George W. Bush’s and Dick Cheney’s opponents in their 2000 and 2004 debate preparations.

But, like anyone McCain might pick, Portman has some negatives that Democrats would be quick to exploit, especially his close ties to George W. Bush at a time when McCain is trying to distance himself from Bush’s record unpopularity. Portman’s hometown paper in Cincinnati once called him “a talking head for the Bush agenda,” and he is not well-known statewide.

But even though Obama and Biden have stepped up their attempts to portray McCain as a Bush clone, they’re also going to have to focus on economic and trade issues, where Portman can more than hold his own.

Portman, who stepped down as Bush’s budget director last year, is an avid outdoorsman and board member of the Nature Conservancy, which would serve him well in dealing with energy conservation and environmental issues. And he’s got a spotless family life that would appeal to Middle America. And although he failed to endorse McCain in 2000 or this year, he said before the March 4 Ohio primary that Republicans would have a better chance of carrying the Buckeye State in November, and with it the presidency, if the nominee is someone like McCain who attracts independents.

Admittedly, Portman is a long shot, but McCain just might decide to roll the dice and create some excitement in the wake of the Democrats’ successful convention in Denver.