LOS ANGELES ? For almost 15 years, Kinde Durkee has been one of the go-to accountants for Democratic candidates in California. She and her firm kept track of expenditures and contributions and made sure that candidates and party committees? campaigns complied with California?s tangled election finance laws.

But just after Labor Day, Ms. Durkee was arrested by the F.B.I. on charges of siphoning hundreds of thousands of dollars from the campaign of a State Assembly member from Orange County for her personal use. The F.B.I. found that Ms. Durkee had control over nearly 400 campaign accounts and had been shuffling money between them ? and out of them ? for years.

The arrest set off a spasm of anxiety among California Democrats, who feared that they might have been victimized in a scandal that many described, with just a tad of exaggeration, as the political accounting equivalent of Bernard Madoff?s Ponzi scheme.

The latest victim ? and so far the most prominent ? was Senator Dianne Feinstein, who is up for re-election next year; aides said as much as $5.2 million might be lost. Mrs. Feinstein joins a cast that includes members of Congress and the State Legislature, as well as local party committees that relied on Ms. Durkee.

?I expect when we learn the magnitude of this crime, it will be staggering to our Democratic community? Eric C. Bauman, the chairman of the Los Angeles County Democratic Party, wrote in a somber e-mail to supporters. ?Already we know that LACDP lost more than $200,000 and several other committees have been cleaned out.?

In an interview, Mr. Bauman said that he had worked with Ms. Durkee for over 15 years, and that he saw her as a member of the Democratic family: someone who was willing to help smaller underfinanced organizations file reports without charge.

?This was not someone who engendered mistrust in any way,? he said.

Representative Susan A. Davis, a San Diego Democrat, told supporters that she had lost over $250,000 in campaign money. ?We have been robbed!!? Ms. Davis wrote, adding, ?As this scandal emerges, she may well become known as the Bernie Madoff of campaign finance treasurers.?

Representative Loretta Sanchez, an Orange County Democrat, lost almost her entire campaign chest, close to $400,000, her aides said.

?Kinde Durkee has been Loretta?s compliance person for 17 years,? said Adrienne Elrod, Ms. Sanchez?s chief of staff. ?While our campaign account is nearly wiped out, we are moving forward and replenishing those funds due to the outpouring support of our supporters.?

According to the complaint filed in her arrest, Ms. Durkee used money she siphoned from campaign committees to pay for her mortgage, her American Express bill, entertainment costs ? including money paid to Amazon.com and Baskin-Robbins ? and the monthly charge for caring for her mother at a Belmont Village assisted-care facility.

Ms. Durkee was arrested on Sept. 2 on charges of mail fraud and was released on $200,000 bond. Her lawyer, Daniel Nixon, did not respond to a call seeking comment.

A spokesman for the United States Attorney?s Office in Sacramento, Lauren Harwood, said it was too early to measure how many clients might have been defrauded, the amount of money involved or whether any of it could be recovered. Ms. Harwood said further charges were likely as the investigation continued.

Ms. Durkee acknowledged much of the wrongdoing in an interview with F.B.I. agents, according to court papers. Speaking of the length of time the activity lasted, Ms. Harwood said, ?She admitted it?s been for years.?

Ms. Durkee is part of a specialized California industry of treasurers who have a command of the state?s campaign finance regulations. As a rule, they tend not to be intimately involved in the campaign itself.

The candidates most at risk are the ones stockpiling money for future campaigns, like Mrs. Feinstein, rather than candidates who are engaged in a campaign and thus have regular amounts of money coming in and out. Mrs. Feinstein?s chief political adviser, Bill Carrick, said the campaign had been unable to get access to, or information from, the bank about the $5.2 million in her campaign account.

?We are trying to figure this all out,? Mr. Carrick said. ?We don?t know what we don?t know.?

Ms. Durkee worked for Mrs. Feinstein in 1992, 1994, 2000 and the 2006 campaign and was working for her at the time of her arrest, Mr. Carrick said. Mrs. Feinstein, though, is known for having a strong network of financial supporters, if she had to replace the money, and is also wealthy.

?What?s distinct about Senator Feinstein is she probably has one of the most impressive lists of campaign supporters of anyone in the country and will have the capacity to go out there and raise the resources that she needs,? said Chris Lehane, a Democratic consultant.

Ian Lovett contributed reporting.