Oct. 9 (Bloomberg) -- Democratic presidential nominee Barack Obama plans to spend what likely will amount to millions of dollars to air a half-hour primetime television advertisement on CBS, NBC and possibly other major networks a week before Election Day.

Obama bought the time on the CBS Corp. network and General Electric Co.'s NBC for Wednesday, Oct. 29, according to spokeswoman Linda Douglass. Obama will appear on News Corp.'s Fox that evening as long as there's no World Series game, she said. The campaign also is in talks to buy air time on Walt Disney Co.'s ABC, said Obama spokesman Bill Burton.

``It's a good opportunity to reach a lot of voters,'' Douglass said.

The Democratic contender will appear in the TV commercial slotted for 8 p.m. six nights before the Nov. 4 election as he seeks to reach tens of millions of voters to persuade them to support him over Republican candidate John McCain. Obama, 47, who has widened his lead in recent national polls, took some media buyers by surprise with the scope of the buy.

``It's got to be in the millions,'' said Chris Werner, partner in LUC Media, a Democratic-leaning political ad-buying firm in Marietta, Georgia, that did not work on the deal.

Campaign officials declined to say what Obama will discuss during the TV ad. ``We're going to be talking about it tomorrow,'' Obama said while visiting a restaurant today in Georgetown, Ohio.

Federal Rules

Under federal rules, the networks must offer similar spots to McCain at the same rate, according to Werner. Political campaigns, under law, pay a discounted amount for ad time.

```The nets will likely call McCain and say, `you want?''' said Werner. ``But one guy may be able to pay for it, and the other guy not.''

McCain spokesman Brian Rogers declined to comment on Obama's TV plans or whether the Republican candidate will pursue a similar strategy.

Independent presidential candidate H. Ross Perot bought 30- minute television ads during his 1992 campaign, drawing audiences of 16.5 million and 10.5 million, according to the Hollywood Reporter.

Obama, an Illinois senator, spent $32.9 million on ads in August, more than half of the $55.9 million he spent in total during the month. McCain spent $40.6 million over the same period, with $18 million going for ads.

Al Gore

The Democratic nominee has been raising funds while on the campaign trail. He raised almost $1 million earlier this week at a post-presidential debate function at the home of former Vice President Al Gore in Nashville, Tennessee. Obama took in almost $10 million last month at two celebrity-filled events in Beverly Hills, California.

Obama raised more than $66 million in August, a one-month record. Still, McCain had about $200 million at the close of the Republican National Convention on Sept. 4, compared to Obama with $95 million. That includes money from both national party committees.

Obama has been able to keep raising money privately because, unlike McCain, the Democrat is not taking taxpayer funds for the general election. Obama is the first major-party nominee to shun public financing since taxpayer money was made available to candidates beginning with the 1976 election.

To contact the reporter on this story: Kim Chipman in Chicago at kchipman@bloomberg.net.

Last Updated: October 9, 2008 20:35 EDT