NORFOLK, Virginia (Reuters) – Democratic presidential nominee Barack Obama launches an unprecedented television blitz on Wednesday to push his economic message on U.S. networks ranging from CBS and NBC to Comedy Central.

Obama's television broadside may also force a 15-minute delay in the Fox network's broadcast of the fifth game of the World Series -- the fiercely-followed championship of Major League Baseball -- coincidentally between teams from Pennsylvania and Florida, both major battlegrounds in the November 4 election.

His Republican rival John McCain plans to appear on CNN's "Larry King Live," hoping to woo viewers with his own vision of the country's future.

Campaign officials said Obama would use the 30 minutes of prime-time air time his campaign has purchased on several networks to focus on his message on the economy, which has taken center stage in his campaign.

"We want to make sure every voter heading into the voting booth knows exactly what Barack Obama would do to bring about fundamental change as president," campaign spokesman Bill Burton said.

A campaign official said the ad would include a video montage, footage of ordinary Americans telling their stories and some live portions of Obama, who is scheduled to be at a rally in Florida that evening.

Obama, already blanketing the airwaves with political advertisements in many battleground states, has purchased the 1/2-hour slot on CBS, NBC and Fox.

The ad, which airs at 8 p.m. EDT, coincides with the anniversary of the October 29, 1929, "Black Tuesday" stock market crash that ushered in the Great Depression.

The cost has been estimated at close to $1 million for each major network slot and reflects the huge cash advantage the Democratic candidate has over McCain.

FIRST SINCE PEROT

The "infomercial" is a throwback to a political advertising strategy common in the 1950s and 1960s. And it marks the first such paid national political telecast since Ross Perot ran a series during his independent bid for president in 1992.

Perot's paid programs, remembered for his use of charts and graphs, drew an average audience of 11.6 million viewers, according to Nielsen Media Research.

Obama, who has shattered all fundraising records, hauled in $150 million for his campaign in September alone. Unlike McCain, Obama chose not to accept public funding for his White House race, freeing him to raise millions privately.

In addition to the major broadcast networks, Wednesday's ad will also air on Spanish-language network Univision, and cable channels including Black Entertainment Television and TV One.

Obama will also appear on the Comedy Central network's popular "The Daily Show with Jon Stewart" on Wednesday, reaching out to younger voters for whom the topical humor show has become a major source of news and ironic commentary.

Rounding out his media campaign, the Democratic candidate is also likely to get coverage for an evening rally in Orlando, Florida, with former President Bill Clinton, the first time the two will campaign together.

The appearances are due to continue. Both NBC and ABC news announced plans to interview the Democratic candidate in coming days.

Obama leads McCain in national polls and in many of the battleground states -- those not considered safely Democratic or Republican -- that will determine the election.

Voters have given Obama higher marks than McCain for his handling of the economy, although the Arizona Republican senator lately has been hammering the Illinois senator over taxes, saying his plan to boost taxes on higher-income Americans would hurt small businesses.

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