Fighting for the lead in South Carolina, John Edwards (search) and John Kerry (search) are pouring even more money into television advertising in the days leading up to Tuesday's primary.

The two senators bought additional airtime starting Friday, which increased their spending for this week in that state to about $300,000 apiece. That's more than being spent by retired Army Gen. Wesley Clark (search), who also is running ads at heavy levels there.

Edwards, a North Carolina resident who was born in South Carolina, has said he must win the state. He has pumped about $1.7 million into TV ads there during his campaign and has been on the air there periodically since August but consistently since November.

Kerry, a Massachusetts senator, started running TV ads in South Carolina this week following wins in Iowa and New Hampshire, which gave him momentum heading into the seven-state challenge that includes South Carolina.

A Zogby tracking poll released Friday shows Kerry and Edwards are competing for the lead, with Edwards having the backing of 25 percent and Kerry of 24 percent. The poll of 600 likely voters was taken Tuesday through Thursday and has a margin of sampling error of plus or minus 4 percentage points. Other candidates, including Clark, were in single digits.

Clark has spent about $2.3 million in South Carolina and has poured about $250,000 in ads into the state this week. He still could purchase more airtime for the weekend.

Edwards, Kerry and Clark are flooding media markets in South Carolina with so many commercials that the TV industry estimates the average viewer would see each candidate's ads eight to 12 times before Tuesday.

Kerry also added to his buys in New Mexico and Oklahoma starting Friday, but Clark is matching him ad-for-ad in those states. Edwards is sticking with both in New Mexico, but running a little less in Oklahoma.

Howard Dean is not broadcasting TV ads now, even though he has spent about $3 million to date in states that hold contests Tuesday.

Joe Lieberman, the Connecticut senator whose campaign is foundering following a fifth-place finish in New Hampshire, did not buy more airtime when his South Carolina and Arizona ad runs ended Thursday. Aides say the campaign has not decided whether to go back on the air there before Tuesday.