Obama's half-hour prime-time commercial airs Wednesday

Barack Obama will focus on the economy and how his tax plans would help the middle class in a half-hour infomercial tonight on most major broadcast networks, except ABC.

The program, scheduled to run on the 79th anniversary of the stock-market crash of 1929, "will share the specifics of Obama's plans to turn the economy around and get the country back on track," campaign spokesman Bill Burton said Tuesday.

ABC at first tried to reach an agreement with the Obama campaign to air the commercial on a different night; by the time the network decided to make tonight available for Obama, his campaign had finalized the ad buy, sources said.

The Obama campaign bought time on CBS, NBC and Fox for $1 million a network, sources said. It was unclear what was paid for the cable-channel time.

Obama is the first presidential candidate since Ross Perot in 1992 to purchase half-hour prime-time slots to get his message across. Obama has the cash to buy the time to drill his message home and answer Republican rival John McCain's criticisms and allegations six days before the election. The Arizona senator had no comparable plans for a national television buy, but he will be interviewed on CNN's "Larry King Live."

Obama also will appear on Comedy Central's "The Daily Show with Jon Stewart" tonight.