WASHINGTON — When conspiracists suggested Friday that the Obama administration had engineered a sharp drop in unemployment to aid President Barack Obama’s re-election, the response was swift.

Career government officials, economists and even some Mitt Romney supporters issued a collective sigh.

The staffers who compute the U.S. unemployment rate work in an agency of the Labor Department. Officials who have overseen the work say it’s prepared under tight security with no White House input or supervision.

“To think that these numbers could be manipulated. ... It’s impossible to do it and get away with it,” said Keith Hall, a former commissioner of the Bureau of Labor Statistics, the agency that calculates the unemployment rate.

“These numbers are very trustworthy,” said Hall, who was appointed by President George W. Bush and whose four-year term ended in January.

The figures that produce the unemployment rate are crunched by several dozen people at the bureau. The only BLS employee appointed by the White House is the commissioner, who operates independently of the White House.

The job is now vacant but is being handled by Acting Commissioner John Galvin, who has worked at the BLS for 34 years.

Yet conspiracy theorists came out in force Friday after the government reported a sudden drop in unemployment a month before Election Day — to 7.8 percent for September from 8.1 percent in August.

Their message: The Obama administration would do anything to ensure a November victory, including manipulating unemployment data. Labor Department officials, joined by Democrats and some Republicans, called the charges implausible.

That didn’t stop the chatter. The allegations were a measure of how politicized the monthly unemployment report has become near the end of a campaign that’s focused on the economy and jobs.

The conspiracy erupted after former General Electric CEO Jack Welch, a Republican, tweeted his skepticism five minutes after the BLS announced the unemployment rate at 8:30 a.m. Eastern time.

“Unbelievable jobs numbers..these Chicago guys will do anything..can’t debate so change numbers,” Welch tweeted, referring to the site of the Obama campaign headquarters.

The drop in unemployment was announced two days after Obama’s lackluster performance in his first debate with Romney.

Republican Rep. Allen West of Florida soon announced via Facebook that he agreed with Welch.

“Somehow by manipulation of data we are all of a sudden below 8 percent unemployment, a month from the presidential election,” West wrote. “This is Orwellian to say the least.”

The Obama administration was forced to defend Labor’s statisticians and economists against accusations that came without supporting evidence.

“No serious person ... would make claims like that,” said Alan Krueger, chairman of the White House Council of Economic Advisers.

The monthly jobs report is prepared with raw data collected by Census workers. The workers interview Americans in about 60,000 households or visit them door-to-door.

People are asked whether they’re employed and, if so, whether their jobs are full or part time. The Census workers gather other information about the respondents’ education, age and gender and ask whether they’re self-employed.

Most of the interviews are done in the week that includes the 19th day of the month. The resulting pile of data is transferred securely by Census to BLS about a week before the jobs report is due.

The office suites where the report is prepared and compiled goes on lockdown. Employees can’t access the area without a hard pass. Staffers working on a paper copy of the report are expected to keep it under lock and key if they aren’t at their desk — even when they go to lunch.

The security isn’t just about keeping the data free of political pressure. The unemployment figures, if leaked early, could improperly move financial markets.

Tom Nardone, a 36-year veteran of the BLS, oversees the report’s preparation. The goal, Nardone said, is to make the report as accurate and “apolitical” as possible.

“We strive to be like Joe Friday, just presenting the facts,” he said.

A draft of the report is completed by early Wednesday before the Friday when it’s released. Several groups of staffers review it. That Wednesday is usually the earliest that the commissioner of the BLS gets involved.

On Thursday afternoon, the report is sent to the White House’s Council of Economic Advisors. Krueger provides a copy to the president.

Hilda Solis, Obama’s labor secretary, doesn’t see the report until around 8 a.m. Friday, a half-hour before its public release.

A week later, Labor releases the raw data on its website. Many academics use the data, which is stripped of all identifying information, for their own research.

The commissioner is the BLS’ only political appointee. And even he or she operates independently of the presidential administration. The Obama administration has selected a new commissioner: Erica Groshen, a vice president at the New York Federal Reserve. She has yet to be approved by the Senate.

On Friday, Romney refrained from discrediting the government data. But plenty of conservatives did that work for him.

Conn Carroll, an editorial writer at the Washington Examiner, tweeted: “I don’t think BLS cooked numbers. I think a bunch of Dems lied about getting jobs. That would have same effect.”

Rick Manning, communications director of Americans for Limited Government and a former public affairs chief of staff at the Labor Department, said “anyone who takes this unemployment report serious is either naive or a paid Obama campaign adviser.”

Rep. Paul Broun, a Georgia Republican, weighed in with a statement saying the report “raises questions for me, and frankly it should be raising eyebrows for people across the country.”

Conspiracy theories are nothing new for Obama. He has been dogged by discredited claims that he wasn’t born in this country and that he is Muslim.

On Friday, one leading Republican sided with Obama’s team in rejecting the latest accusations.

“Stop with the dumb conspiracy theories. Good grief,” Tony Fratto, a strategist who was a top communications official in the Bush White House, tweeted.

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Mayerowitz reported from New York.

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Scott Mayerowitz can be reached at http://twitter.com/GlobeTrotScott . Christopher S. Rugaber can be reached at: http://twitter.com/ChrisRugaber .

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