WASHINGTON, D.C. — The nation’s federal debt by the end of the year will reach the highest level since shortly after World War II and is on pace to reach historic and unsustainable levels within 30 years, according to a government report released Tuesday.

The federal debt already equals 78% of the nation’s gross domestic product. It is on track to reach 92% by the end of the next decade and 144% by 2049, according to calculations compiled by the Congressional Budget Office.

Phillip L. Swagel, director of the nonpartisan agency responsible for putting together budget estimates for Congress, warned that the rising debt poses “substantial risks for the nation and presents policymakers with significant challenges.”

“High and rising federal debt increases the likelihood of a fiscal crisis because it erodes investors’ confidence in the government’s fiscal position and could result in a sharp reduction in their valuation of Treasury securities,” the report says.

The report paints a slightly better picture than the estimates released last year — debt is projected to grow more slowly — because of changes to the agency’s projections and other spending changes.

The CBO warns that its estimates are subject to substantial changes, including new policies from lawmakers, economic changes and interest rates.