“They are trying to throw out these codes,” said Representative Gregory Meeks, a Democrat from New York.

“He’s ‘not one of us?’” Mr. Meeks said, referring to a comment Sarah Palin made at a campaign rally on Oct. 6 in Florida. “That’s racial. That’s fear. They know they can’t win on the issues, so the last resort they have is race and fear.”

“Racism is alive and well in this country, and McCain and Palin are trying to appeal to that and it’s unfortunate,” said Representative Ed Towns, also from New York.

In recent days, as polls have shown a steady lead for the Democratic ticket, Mr. McCain and Ms. Palin have used reports of Mr. Obama’s loose association with Bill Ayers, a former member of the ’60s radical group the Weather Underground, as evidence that he is different from them.

“Our opponent,” Ms. Palin told donors in Englewood, Colo., “is someone who sees America, it seems, as being so imperfect, imperfect enough, that he’s palling around with terrorists who would target their own country.”

She added, “This is not a man who sees America like you and I see America,” she said. “We see America as a force of good in this world. We see an America of exceptionalism.”

An Associated Press analysis characterized those remarks as “unsubstantiated” and carrying “a racially tinged subtext.”

Neither Mr. McCain nor Ms. Palin has backed off the line of attack.

Again invoking Mr. Obama’s intermittent encounters with Mr. Ayers, Mr. McCain asked a crowd in Albuquerque, N.M., on Oct. 6, “Who is the real Barack Obama?” Someone in the crowd screamed in reply, “a terrorist!” Mr. McCain grimaced, but kept going.

Before Ms. Palin took the stage in Estero, Fla., at the Oct. 6 event, one of the introductory speakers, Mike Scott, the sheriff of Lee County, referred to the Democratic candidate as “Barack Hussein Obama,” a practice the McCain campaign has distanced itself from in the past. Apparently, no longer. Ms. Palin also said that she had advised Mr. McCain to “take the gloves off” and said Mr. Obama was “not one of us.”

David Bositis, senior political analyst at the Joint Center for Political and Economic Studies and an expert on African-American issues, said that most Americans were too busy worrying about their economic future to concentrate on Mr. McCain’s comments on the stump. To the extent that people were listening, though, he said his remarks would be “not just crossing the line but introducing serious ugliness into the race.” 

Other black members of Congress, all Democrats who support Mr. Obama, said they were dismayed by the new and vicious tenor of the McCain attacks.

“If McCain’s attacks don’t cross the line, they’re certainly teetering on it,” said Representative Jesse Jackson Jr. of Illinois. “He is certainly appealing to people’s fears and not their hopes.”

Mr. Jackson took issue with the McCain campaign’s attack on Mr. Obama’s connection to Mr. Ayers, who committed acts of domestic terrorism when Mr. Obama was 8 years old, and contrasted that with Mr. McCain’s long relationships with erstwhile supporters of segregation in the Senate like Jesse Helms and Strom Thurmond.

“Should McCain be held responsible for having served with segregationalists when he was 8 years old, 18 years old, 28 years old, 38 years old, 48 years old, 58 years old, 68 years old?” Mr. Jackson said. “Did he ever meet with any of them? Did he ever conference with them or work with them? Did McCain quit the Senate instead of work with them?”

He added: “Did Sarah Palin throw her husband out of the house for advocating secession from the union?”

“I guess they are suggesting that he is a terrorist; it’s just patently absurd,” said Representative Bobby Scott of Virginia. “John McCain himself said he wouldn’t participate in such things, but I guess that changes when you’re losing.”

“Some may say their true colors are showing,” said Representative Yvette Clarke of New York. “Others may say they’re just not being thoughtful. But certainly a lot of the language I’ve heard I consider to be incendiary. I believe it is meant to generate a certain sentiment within their base that engenders fear and certainly appeals to a group of people within our society who would pursue this along racial lines.

“It’s very clear,” she said.

Ms. Clarke also found a racial subtext in Ms. Palin’s repeated appeals to “Joe Six-Pack” and “hockey moms.”

“Who exactly is Joe Six-Pack and who are these hockey moms? That’s what I’d like to know,” she said. “Is that supposed to be terminology that is of common ground to all Americans? I don’t find that. It leaves a lot of people out.”

New York State Senator Bill Perkins, an early supporter of Mr. Obama, said, “They are obviously playing on people’s fears and prejudices in a desperate way. While not explicitly relating to race, they are clearly creating the opportunity for those inclined to come to those conclusions. I think it is going to become more explicit as we move forward. It’s subtle now, but not so subtle as to be mistaken.”

And Kevin Parker, a New York state senator from Brooklyn, said, “If you have to remind people that Barack Obama is African-American, you have reached the bottom.”

In response to the Obama supporters’ comments, McCain campaign spokesman Peter Feldman provided the following statement: “It is disappointing that Barack Obama and his supporters continue to play the race card from the bottom of the deck. This is a tactic that the Obama Campaign has used before, and which McCain campaign manager Rick Davis correctly called ‘divisive, shameful, and wrong.’ It is legitimate for John McCain to ask questions about Barack Obama’s relationship with the unrepentant domestic terrorist William Ayers because Senator Obama has not been truthful about this relationship.  Many Americans want these questions answered. Despite the fact that Barack Obama has been running for president since joining the Senate, many Americans are still wondering, ‘who is Barack Obama?’ These comments are a sure sign of a flailing campaign that refuses to be honest with voters and that is bordering on desperation.”

The Obama campaign did not respond to requests for comment by deadline.

jhorowitz@observer.com