WASHINGTON—The Congressional Budget Office today warned the nation’s public debt load is projected to hit dangerously high levels by September - roughly 70 percent of the nation’s gross domestic product - a figure not seen since World War II, underscoring the crucial decisions facing Washington and the candidates in this presidential election year.

The report from the nonpartisan budget office throws into stark terms the challenges facing the U.S. economy and the dangers of congressional inaction. Allowing debt levels of that size to grow would ripple across the economy in years to come, slashing gross domestic product and threatening a fiscal crisis.

At the same time, the CBO has warned that any attempt by politicians in Washington to quickly bring the budget into balance with new taxes or spending cuts carries its own risks: Such sudden moves, as lawmakers are considering for the end of this year, could throw the economy into a recession in 2013, the budget office said last month.

Once again, a measured approach appears to be the best route.

“The explosive path of federal debt under the alternative fiscal scenario - which maintains what might be deemed current policies - underscores the need for large and timely policy changes to put the federal government on a sustainable fiscal course,” the report said.

“Policymakers will need to increase revenues substantially above historical levels as a percentage of GDP, decrease spending significantly from projected levels, or adopt some combination of those two approaches.”