WASHINGTON – People and businesses underpaid their taxes by an estimated 17 percent in the most recent year studied, meaning they failed to send the government $450 billion it was owed, according to an Internal Revenue Service report released Friday.

The study covered 2006, the most recent for which the IRS said it had data available. The amount of underpaid taxes far exceeded the size of the entire federal budget deficit at the time.

After IRS audits and other enforcement efforts, non-compliance shrank to 14 percent, leaving the final amount of unpaid taxes at $385 billion.

That is still larger than the budget deficit for fiscal 2006, which was $248 billion. Fiscal years begin in October of the previous year.

Altogether, the IRS estimates it was owed nearly $2.7 trillion in taxes in 2006.

The IRS has made efforts to improve compliance, such as increasing oversight of professional tax return preparers and increasing the information that must be reported to the agency by stock brokers, mutual fund companies and for some business transactions.

Even so, tax analysts said there was no reason to believe that today’s compliance rate has changed significantly from the 2006 figures. That is chiefly because significant portions of the underpaid taxes are believed to come from businesses and individuals who report information about their income that is difficult for the IRS to verify.

“It’s hard to get to that,” said Clint Stretch, a tax policy expert for Deloitte Tax LLP. “Nobody wants a bunch of IRS police hammering on small business people.”