For U.S. Rep. John P. Murtha, it was the kind of throwaway line common to a congressional veteran known as equal parts cagey and blunt -- a hammer blow of an opener followed by an explanation lost amid the reverberations.

"There's no question Western Pennsylvania's a racist area," Mr. Murtha said, predicting that Democratic nominee Barack Obama would face difficulty attracting some voters in this state. He quickly explained that the legion of older voters in the region were slow to warm to change, but that they were coming around.

In a state already roiled by the very mention of race and its effect on the electorate, Mr. Murtha, an ex-Marine and one of the power brokers of the House, achieved the political equivalent of tossing a grenade into the supply depot.

"When I say racist area, you know, the older people are hesitant -- they're slow in seeing change, real change," Mr. Murtha said in a meeting with Pittsburgh Post-Gazette editors. "It's better, though, than it was two or three months ago. Two or three months ago it was bad.

"I had a World War II veterans rally, this was maybe three or four months ago, they're all telling me 'I'm not voting for Obama.' They're all Democrats. I've got a heavily Democrat district. I don't hear that now. I think the economic situation's changed that."

The reaction to Mr. Murtha's remarks was swift, dramatic, angry and as wide-reaching as the Internet.

Across the political spectrum, from the right-leaning Breitbart.com to the liberal HuffingtonPost.com, the Web crackled.

Much of the dismay over Mr. Murtha's remarks came not over the question of truth or falsity, but the reinjection of race into the contest in a place that had already wrestled unpleasantly with the subject. In the spring, a passing remark by Gov. Ed Rendell that Mr. Obama's race might work against him in some quarters triggered a row. Those comments came on the heels of racially tinged primaries in South Carolina and West Virginia.

"You're saying it at the wrong time and it charges up the atmosphere and distracts away from the issue," said Bob Guzzardi, a conservative Web activist who quickly went on the attack, saying Mr. Murtha had "smeared" his political base.

"You have to ask yourself what compels him to do this at this time," added Bob Sklaroff, a suburban Philadelphia oncologist and political activist who monitored both Web and cable news traffic as Mr. Murtha's comments bounced across the nation.

"You ever heard of a self-fulfilling prophecy?" said Dr. Sklaroff. "When you say something like that, you often will implant that idea in some people."

Yesterday, Mr. Murtha issued an apology for his comments.

"While we cannot deny that race is a factor in this election, I believe we've been able to look beyond race these past few months and that voters today are concerned with the policy differences of our two candidates and their vision for the future of our great country," he said.

Then, without issuing a statement, he begged off on the lone debate scheduled between him and his opponent in the Nov. 4 congressional election, Republican Bill Russell.

When Mr. Rendell, in his own comments to the Post-Gazette, casually suggested that Mr. Obama would lose votes because of his race -- as well as compensate by the new voters he'd brought on board -- an uproar ensued for several days.

Mr. Murtha's remarks, according to one authority, would have seemed innocuous save for the freighted word "racist."

"He picked a classification that was too loaded. Everything he said after that was what he meant," said James Alexander, a professor of political science at Mr. Murtha's alma mater, the University of Pittsburgh at Johnstown.

Mr. Alexander, who has spent three decades at the Pitt Johnstown campus and who has studied the ethnic history of the town, said Mr. Murtha was essentially describing a populace less hostile to a black candidate than simply uncomfortable because of unfamiliarity.

In a town where generations of Irish, Germans, Italians and Slavs kept studiously separate identities well into the 1970s, Mr. Murtha's description of the region as "racist" takes on a different meaning, he said.

"He's not sophisticated enough to realize people are going to hear that word in different ways," Mr. Alexander said. "You're talking about a clannishness without the 'K' -- it's a clannishness among ethnic groups."

Mr. Murtha's home base is Cambria County, a region steeped in ethnic divisions fed by succeeding waves of European immigrants. Its black population consists of African-Americans who migrated from the south to its steel center of Johnstown in the early part of the 20th century. So segregated was the city that in 1923, then-Mayor Joseph Cauffiel ordered the wholesale expulsion of black residents.

At the same time, the 12th Congressional District, which has been reconfigured over the past 30 years, but has always had its heart in Johnstown, has been overwhelmingly Democratic and economically liberal. Until George W. Bush narrowly carried Cambria in 2004, the county had not voted for a Republican for president since the McGovern debacle of 1972.

Mr. Murtha had faced that issue before. In 1977 his hometown was struck by a devastating flood that killed more than 80 people and left thousands in the city's floodplain neighborhoods without homes. The Federal Emergency Management Administration set up camps of mobile homes on the high ground of neighboring suburbs and the arrival of city residents -- some of them black -- was met with resistance in places like Richland Township.

At an acrimonious meeting at the township's junior high school, the young Mr. Murtha faced them down, demanding from one man that he explain his objections to these new arrivals.

Some of it, say observers, was race. More potently, it was the arrival of low-income people into the new-money suburbs.

"To really understand Johnstown, the issue here is class, not race," said Richard Burkert, a local historian who oversees the region's flood museum. "The people in the valley don't trust people on the hill."