May 29 (Blo****erg) -- In 2006, Ohio Republican Representative Steve Chabot barely survived the electoral drag of the Iraq War, congressional scandals and an unpopular president. Barack Obama's presidential candidacy this year may deliver a knockout blow.

More than a quarter of the voters in Chabot's Cincinnati district are black, the highest concentration for any incumbent House Republican in a competitive race this fall. Obama's likely spot at the top of the Democratic ticket may fuel a surge in turnout among black voters that could help the party pick up a half-dozen new House seats.

There has already been record turnout of black voters in this year's primary contests. The Obama campaign and political experts expect that trend to continue in the fall, imperiling incumbents in Republican-held House districts that have a double- digit black vote.

``You'll see a record proportion of the vote in each district that is African-American,'' said Dave Wasserman, House editor of the nonpartisan Cook Political Report in Washington.

Chabot's district gave President George W. Bush only a little more than 50 percent of its vote in 2004. Still, Chabot said he is confident he will win re-election against Democrat Steve Driehaus.

`Battle-Tested'

``We're battle-tested and we've been through this many times before,'' Chabot, 55, said in an interview. ``Nobody's going to sneak up on us.''

Chabot, who is serving his seventh term, said he expects record voter turnout for both parties, and any boost Obama or presumptive Republican nominee John McCain may give to other candidates will balance out.

Democratic candidates have already benefited from Illinois Senator Obama's coattails in recent special elections in Mississippi and Louisiana, where the party picked up two House seats, said David Bositis, an expert on black voting trends at the Joint Center for Political and Economic Studies in Washington.

The Louisiana seat, won in April by Democrat Dan Cazayoux, is in a district where one-third of voters are black. This month, in Louisiana, Democrat Travis Childers won a district where almost a third of voters are black.

That trend will accelerate this fall, Bositis said.

`Money Machine'

``Obama is a limitless money machine, and they are going to put an enormous amount of effort into registering people,'' he said.

To be sure, Obama, 46, could be a drag on some of his party's incumbents, particularly in states with a heavy representation of white working-class voters who make less than $50,000 a year and don't have a college education. In primaries in Kentucky and Ohio, those voters preferred Obama's Democratic rival, Senator Hillary Clinton of New York, by a 2-to-1 margin.

At the same time, Wasserman said Obama's presence on the ticket could help Democrats capture House districts with a large black voter presence, including those of incumbent Republicans Chris Shays of Connecticut, Robin Hayes of North Carolina and Thelma Drake of Virginia. The seats of retiring Republicans Jim McCrery of Louisiana, Tom Davis of Virginia and Terry Everett of Alabama also are vulnerable, he said.

Ohio Primary

While Obama lost Ohio's Democratic primary in March, his strongest showing in the state was in Chabot's district, where he took 62 percent of the vote.

Wasserman said the black vote in the district could shoot to as high as a third of ballots cast in 2008 from more than a quarter in 2004. That could yield as many as 20,000 votes; Chabot won his last election by 9,100 votes.

Driehaus, a state legislator, is trying to win over black voters. Memorial Day weekend, he helped lead a parade through the streets of Evanston, a predominantly black neighborhood, darting onto sidewalks and front porches to greet voters.

Obama has ``people coming out like I've never seen,'' said Driehaus, 41.

Chabot said Obama's pull is exaggerated. Many voters who participated in the Democratic primary would ``come home'' to the Republicans in the general election as they become familiar with Obama's liberal policies, he said.

Driehaus, like Chabot, is anti-abortion and Catholic, and he said he hopes to peel away some of the voters in western Cincinnati's heavily Catholic neighborhoods who have been central to Chabot's wins in the past. A third of the white vote, c****ined with high turnout among black Democrats, would allow him to win the seat.

Black Turnout

In Chabot's district, black voters said Obama is powering a surge of interest.

``This may be the first and last time a black person will get this close to the presidency,'' said Lamar Wright, 22, a black student who didn't vote in 2004.

So far, Chabot has out-raised Driehaus. On March 31, he had $1.1 million left to spend, compared with Driehaus' $567,000. Voters of both races and parties praised Chabot, though some who backed him in the past said they haven't decided whether to do so this year.

Some voters said Chabot -- who supports the Iraq War -- is too closely tied to Bush, and many blacks said they are likely to vote a straight Democratic ticket.

``I know people who have never been interested in politics who are voting'' for Obama, said Aaron Martin, 31, a barber and Obama supporter in Cincinnati.