WASHINGTON — Representative Mark Schauer of Michigan does not dwell on the legislation he has voted for during his first term in Congress, which includes the Democratic stimulus plan and health insurance overhaul. But he reminds his constituents what he has fought against, declaring, “I must ask myself 10 times a day, what is Washington thinking?”

Representative Glenn Nye of Virginia does not mention in his television advertisements that he is a Democrat. But he expresses a deep worry about the national debt, saying, “I stood up to my party leaders and voted no.”

Representative Suzanne M. Kosmas of Florida looks straight into the camera during her latest commercial and declares, “People in this district are mad, and I’m mad, too.”

The advertisements from these three vulnerable Democrats offer a window into the party’s strategy to try to keep control of the House in November at a moment when Republicans and their allies are substantially outspending Democrats and their backers.

Two years after arriving in Washington on a message of hope and change, Democratic candidates are not extolling their party’s accomplishments, but rather distancing themselves from their party’s agenda.

The midterm elections may revolve around a series of big issues, particularly with control of Congress at stake. But a look at the advertising themes and images being employed by Democrats shows all the ways they are trying to personalize their contests and avoid being defined as ideological partners of President Obama’s or as part of the Washington establishment.

In the last six weeks, Republicans have outspent Democrats $20 million to $13 million in television advertising, according to an analysis by The New York Times of 56 of the nation’s most competitive House and Senate races. The Republican advantage includes $9 million in spending from outside groups, compared with $3 million from left-leaning interests.

The disparity in spending, particularly from third-party groups, is the central reason Mr. Obama has agreed to step up his fund-raising efforts for the party in the coming weeks, aides said, and why Speaker Nancy Pelosi is asking leading donors to dig deeper.

The images of Mr. Obama and Ms. Pelosi appear with more frequency than those of any other political figures — but nearly always in Republican advertisements. They have been mentioned so many times that in their advertising some Democrats have started calling out their Republican rivals, including Representative Roy Blunt of Missouri, who is running for the Senate.

“Congressman Roy Blunt seems to think he’s running for the Senate against Barack Obama and Nancy Pelosi,” says Robin Carnahan, the Democratic candidate, standing in the middle of a cow lot on her farm. “Hey Roy, you’re running against me!”

For all the evolutions in technology, with voters able to gather information instantly about candidates from an ever-widening array of sources, television advertising remains the most central ingredient of political races. Many candidates say they are buying more spots than in previous election cycles, hoping to break through to viewers who often tune out the first few times they come across a commercial.

The voices of politicians, along with soothing-sounding narrators talking about the economic stimulus, federal spending and bank bailouts, resonate from television sets throughout the morning, afternoon and evening.

In the last six weeks alone, Republicans broadcast 45,100 commercials and Democrats broadcast 38,400 in the competitive races included in the Times analysis of advertising data collected by the independent Campaign Media Analysis Group.

“The political response to a fragmented media world is to talk louder and longer,” said Evan L. Tracey, president of the group, which monitors political advertising. “This will be the most negative election we’ve probably ever seen, because everyone is trying to tap into voters on an emotional level and no one is looking to entertain right now.”

Many of the most serious and stark messages come in advertisements sponsored by Americans for Prosperity, an advocacy group financed in large part by David Koch, who invests millions of dollars on behalf of conservative causes. The group has focused on a handful of races, spending $1.5 million in seven competitive House seats in the last six weeks, leaving the Democratic candidates under fire at all hours of the day on television.

“To small businesses, Betsy Markey is the same as Nancy Pelosi,” a man says in one of the advertisements, referring to Representative Betsy Markey, Democrat of Colorado. For a one-week stretch in August, the group ran $40,000 worth of commercials every day against her.

In Florida, Marco Rubio, the Republican candidate for the Senate, has spent $1.1 million over the last six weeks on advertisements that are largely positive and biographical, telling the story about how he is a first-generation American of Cuban heritage. Yet in the closing moments of his spots, he says he is worried about his children’s future.

“As the son of exiles, I understand what it means to lose your country,” Mr. Rubio says. “I approve this message because we can’t afford to bankrupt ours.”

Senator Harry Reid of Nevada barely appears in many of his commercials. In one of his latest, he said nothing about his time as majority leader, but instead talked about milk. A dairy owner offered a testimonial that Mr. Reid “really came through for us.”

A review of hundreds of advertisements broadcast over the last six weeks found that Republicans were more than twice as likely to talk about jobs, often criticizing Democrats as not creating them. Republicans also mentioned health care far more than Democrats did. And when Democrats do bring up the issue, 38 percent of the commercials are critical of the new law.

“I’ve said no to more government spending, no to President Obama’s big health care plan and no to Wall Street bailouts,” Representative Walt Minnick, Democrat of Idaho, said in a solemn voice, sitting on the front steps of a house in jeans and shirtsleeves, looking as if he is worlds away from Washington.

The themes on display in the advertising campaigns reflect months of polling and focus groups by candidates in both parties. Democrats were twice as likely to mention financial regulation or Wall Street, according to the analysis, while Republicans mentioned the budget or government spending nearly twice as often as Democrats.

With Democrats holding a 39-seat majority in the House and Republicans 10 seats short of a Senate majority, there are more Republican candidates introducing themselves as outsiders, without the need to defend their voting records in Washington. But for the few seats where Democrats are aggressively trying to knock off a Republican incumbent, the spending argument has also been deployed.

A Democratic candidate in Nebraska’s Second District, Tom White, is urging voters to consider that Representative Lee Terry, a Republican, is to blame for the size of the debt.

“Every day, every child in America grows deep and deeper in debt, thanks to Washington politicians like Lee Terry,” said the advertisement sponsored by Mr. White, who does not mention that he is a Democrat, branding himself “Nebraska Independence for Congress.”

With early voting beginning in several states in a few weeks and with Election Day less than two months away, some of the most vulnerable Democratic candidates have turned to another approach: pleading for a second chance.

“I’ve made my share of mistakes, but they were honest mistakes, and I’ve listened to your concerns and I’ve grown on the job,” said Gov. Chet Culver of Iowa, wearing a solemn expression that gives way to a slight smile. “I hope you give us the chance.”

Amanda Cox contributed research.