Democratic presidential hopeful Howard Dean (search) is doubling his ad spending in Iowa - to at least $400,000 over 10 days - in an attempt to pull away from rival Dick Gephardt (search) in the key early voting state.

Gephardt's campaign accused Dean of trying to "buy the Iowa caucuses" with the new 60-second biographical ad slated to start airing Monday throughout the state.

Dean's power play puts pressure on Gephardt because it is unclear whether the Missouri congressman can match or exceed the former Vermont governor's buy. Gephardt is slated to spend less than half of that - about $160,000 - during the same period.

Dean can spend as much as he wants in the Jan. 19 caucus state because he is not accepting public financing. Gephardt is taking the government money, so he must abide by state spending caps.

Polls indicate that Dean is in a tight race with Gephardt for the Iowa caucuses. He holds a wide lead in the follow-up primary in New Hampshire, and is widely considered the front-runner for the Democratic nomination.

Dean usually buys airtime in $200,000 spurts, but is pouring $400,000 to $500,000 into Iowa TV stations to air the new 60-second spot along with a 30-second ad already on the air there. It's the largest ad buy in the state to date, according to two senior officials in Dean's campaign who spoke on the condition of anonymity.

One aide said the new spot - the first biographical ad of his campaign - seeks to broaden voter understanding of Dean. At 60 seconds, it is twice as long as a standard ad and twice as expensive. The buy is so large that the average Iowa TV viewer could see Dean commercials 18 times over 10 days.

The biographical ad shows Dean as a husband, family doctor and lieutenant governor. It talks about him taking classes at night to get into medical school, working in an emergency room in the Bronx with his wife, Judy, and becoming governor "under the worst of circumstances" when Gov. Richard Snelling (search) died of a heart attack in 1991.

An announcer says that as governor, Dean "earned a reputation as a maverick and independent by turning a deficit into a surplus, creating jobs, raising the minimum wage twice and balancing budgets 11 years in a row."

The buy also includes a 30-second ad, titled "Momentum," that is running in Iowa this week. Using the slogan "There's something happening out there," the ad includes footage from Dean's "Sleepless Summer" tour (search), a four-day August campaign swing that drew thousands and raised $1 million on the Internet.

Bill Carrick, Gephardt's media adviser, said the buy proves that Dean's decision to opt out of the public financing system had nothing to do with challenging President Bush next year.

"It's evidence that it always had to do with him spending way more than the cap in Iowa," Carrick said. "He's trying to buy the Iowa caucuses."

A Dean spokeswoman said that's not true.

"We have said all along that we have to be able to compete with this president," said Tricia Enright. "The fact of the matter is that George W. Bush can begin airing ads against the Democrats whenever he wants to."

She said the Republican National Committee (search) proved that this week when it aired an ad in Iowa that suggests Democrats are retreating from the fight against terrorism.

Dean has spent about $1.8 million on ads in Iowa, compared with about $1.2 million spent by Gephardt, who was absent from the airwaves for two weeks earlier this month.

Dean's buy follows two weeks in which competition between the two campaigns grew increasingly fierce on the ground and on the air.

Last week, Dean started running an ad that took Gephardt to task for backing President Bush on the Iraq war. Gephardt responded with his own spot accusing Dean of flip-flopping on the issue of Bush's request for $87 billion to rebuild Iraq and Afghanistan.