President Barack Obama has preached that all Americans should pay their fair share in taxes, but a government report finds that tens of thousands of federal employees — from staffers in Congress to federal agencies and even Obama’s executive office — collectively owe the government billions in back taxes.

Data from the Internal Revenue Service found that more than 279,000 federal employees and retirees owed $3.4 billion in back income taxes as of Sept. 30, 2010.

The data showed that 467 employees of the House of Representatives, or about 4.2 percent of the workforce, owed more than $8.5 million. In the Senate, 217 employees, or about 3 percent of the workforce, owed $2.13 million.

Obama’s staff was not immune, either, with 36 people in Obama’s executive office of nearly 1,800 workers — about 2 percent — owing the government $833,970 in back taxes.

Obama used part of his State of the Union address Tuesday night to promote economic fairness, arguing for changes in the tax code that would create a minimum tax rate of at least 30 percent on anyone making more than $1 million. The finances of one of his chief Republican rivals, Mitt Romney, has been scrutinized because he, like many millionaires, pays a lower rate because most of his income came from investments, which are taxed at a lower rate.

The IRS report attracted the attention of Republicans, who said it undercut the president’s argument on taxes. “If Obama wants people to pay their ‘fair share,’ perhaps he should start with his own staff,” tweeted Republican National Committee chairman Reince Priebus.

White House officials noted that the delinquency rate among executive office staff had fallen from nearly 3 percent in 2008. In 2009, 41 employees in the president’s executive office owed about $830,000, representing about 2.3 percent of its workforce.

White House spokeswoman Amy Brundage said the annual report was released by the IRS because there is a “high standard for government employees.”

“Though the report shows that fewer executive office employees owe taxes than in the last year of the previous administration and we expect all employees to pay their taxes in full, more needs to be done to ensure compliance and the president has asked his team to work on this issue,” Brundage said.

Overall, the total amount owed is down slightly from September 2009, when more than 282,000 federal workers owed $3.3 billion in taxes.

The report does not offer specific explanations for the delinquencies. Many people who owe back taxes file returns but cannot pay the full amount when their taxes are due, said IRS spokesman Anthony Burke. Others may be disputing the bill, may have filed jointly with a spouse who owes taxes or may have had their tax bills increased by an audit and cannot pay the higher amount.

The statistics on federal employees do not include those who are on payment plans. The IRS doesn’t provide a comparable delinquency rate for income taxes paid by the public.

Among Cabinet agencies, the departments of Education and Housing and Urban Development had the highest delinquency rates, at nearly 4 percent. The Treasury Department had the lowest delinquency rate, at nearly 1 percent.