The national debt is on pace to keep growing over the next 20 years and eventually become three times the size of the U.S. economy, the government's top auditor warned lawmakers Wednesday.

"The federal government remains on a long-term unsustainable fiscal path," Government Accountability Office Comptroller General Gene Dodaro said during a Senate Budget Committee hearing.

Entitlement programs such as Social Security and Medicare drive those numbers, along with interest payments on the federal debt. Sen. Ron Johnson, R-Wis., estimated those factors will contribute to a $103 trillion national debt over the next 30 years. Dodaro concurred, but his testimony underscored that lawmakers neither have a consensus about what the debt level should be, nor how to achieve that goal.

Dodaro and Johnson presented the debt problem in somewhat different terms, over varying time periods, but the comptroller general said the long-term point is the same.

"These projections go to 200 and 300 percent and even higher of debt held by the public as a percentage of gross domestic product," said Dodaro. "We're going to owe more than our entire economy is producing and by definition this is not sustainable."

That confirms the worst fears of the budget hawks who have challenged President Obama in recent years, but Dodaro also criticized attempts to use debt limit standoffs as a means of forcing fiscal restraint. "People are actually avoiding borrowing treasuries that might mature during the debt ceiling issue," he said. "And it's causing liquidity problems in the secondary market, and it's adding to the interest that the federal government has to pay on the debt."

Dodaro suggested that Congress set a debt limit during the budget process — "It needs to be brought closer to where the actual spending decisions are made by the federal government," he said — but that will require overhauling how Congress approaches fiscal policy.

"The debt management issues at the federal level have never really been modernized at all," he said.