With just five days to go until Iowa Democrats hold their pivotal caucuses, front-runner Howard Dean (search) on Wednesday found himself in a much tighter race, new polling showed.

Dean, the former Vermont governor, was the favored choice of 24 percent of Iowa Democrats while Rep. Dick Gephardt (search) of Missouri and Sen. John Kerry (search) of Massachusetts each took 21 percent, according to a daily tracking poll by Zogby International (search).

Coming in fourth is Sen. John Edwards (search) of North Carolina with 15 percent.

Because the poll has a 4.5 percent margin of error, the results mean that all four men have a shot to win, said pollster John Zogby.

"Kerry now leads among liberals, while moderates belong to Gephardt. The three candidates are bunched together among Democrats. Dean still leads among voters under 50, and Gephardt dominates voters over age 65," he said.

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Iowa is not the only place where Dean is feeling the heat. New polls in New Hampshire, which holds its primary Jan. 27, eight days after the Iowa caucuses, also suggest that the race there may be tightening.

Private polling by two campaigns in the Granite State showed that Dean's lead has shrunk to single digits from a first-of-the-year high of about 25 percentage points, according to officials familiar with the polls.

However, an independent poll, by the American Research Group, Inc. (search), showed Dean with 34 percent support and retired Gen. Wesley Clark (search) with 20 percent in the three-day period that ended Monday, far ahead of the rest of the field.

Clark was not campaigning in Iowa but others in the field of nine Democrats were stumping hard for votes.

Dean was airing a new anti-war ad in Iowa. "Where did the Washington Democrats stand on the war?" an announcer says in Dean's ad, which drew protests from his rivals. "Dick Gephardt wrote the resolution to authorize war. John Kerry and John Edwards both voted for the war."

Clark was spared criticism in the ad, but officials familiar with Dean's strategy said the retired Army general is about to become a campaign target.

Dean on Wednesday continued to emphasize his position as the lone Democratic candidate that was against the war in Iraq.

"I got my start in this race by standing up to George Bush when he supported a war 70 percent of the people agreed with him on because he didn't tell the truth about how we got there," Dean said. "We're going to continue to remind people that when it was important to stand up to George Bush, only one candidate in this race dared to do it."

At least one rival warned that Dean's more aggressive stance could backfire with voters weary of assaults.

"What people are hungering for here in Iowa is a positive, uplifting campaign of hope, which is what my campaign is about," said Edwards.

The decision to shift gears came at a high-level meeting on Monday in which Dean was urged by top advisers to revert to his earlier message that had moved him from an obscure former governor of Vermont to a front-runner.

They warned Dean this was no time to be cautious, and the new pitch was described as: "This campaign is about the people against the establishment and you are the people."

Dean also has developed an aggressive damage-control strategy designed to confront potential problems before they blow out of proportion.

An example of that came last week when Dean claimed a prized endorsement from four-term Iowa Sen. Tom Harkin. Participants in that decision said Harkin notified Dean by phone Thursday night that he had decided to endorse. Within hours, a story broke of a videotape in which Dean said the caucuses are dominated by special interests.

Knowing the sensitivity of the issue in Iowa, where the leadoff caucuses are a prized event, Dean quickly called Harkin again, giving him a chance to change his mind if the flap proved embarrassing.

After examining a transcript of the exchange, Harkin decided to move forward, and the endorsement was announced Friday.

Fox News' Steve Brown and The Associated Press contributed to this report.