-By Steve McClellan

NEW YORK The potential for a return to TV advertising in presidential politics was raised last week after Democratic contender Barack Obama opened his campaign war chest and earmarked $5 million for ads during NBC's coverage of the Beijing Olympic games next month. Sources said Republican candidate John McCain has also talked to NBC about a possible Olympics buy, but has no deal yet for any network spots.

According to analysts, the Obama buy was the single biggest purchase of ad time by a presidential candidate on broadcast network TV in perhaps three decades, "It's pretty unprecedented," in recent modern campaigning, said Evan Tracey, COO of TNS Media Intelligence Campaign Media Analysis Group.

Presidential candidates in recent times have spent most of their ad dollars on local TV, radio and cable, enabling them to focus on key "battle grounds" where the race is close.

But Tracey cites several factors that could result in a resurgence of network spending. Obama in particular is flush with cash, raising roughly $70 million in May and June alone, he said. The Olympics, with its huge audience (almost 25 million nightly viewers tuned into the 2004 Athens Olympics on NBC, per Nielsen Media Research), "fortifies what he will do at the state and local level," said Tracey, "The buy may be a toe in the water for using more network TV in the fall."

One lesson learned from the Bush campaign four yeas ago: don't politicize the Olympics. Bush bought a spot on cable during the Athens Games that talked about how some day Iraq would have an Olympic swim team. "It was universally panned," Tracey said. "So Obama has to strike the right chord, or he will be criticized."

Tracey predicts that a record $800 million will be spent on presidential campaign ads for this election, 60 percent more than in 2004.

Officials at Obama's media shop, GMMB, and his creative agency, AKPD, either couldn't be reached or didn't return calls.