WASHINGTON – President Obama is roundly criticized by Republicans for running up the nation’s debt. But if a Republican takes the White House, the debt will keep climbing — and perhaps even faster than under Obama’s proposed policies, a budget watchdog group says.

GOP presidential hopefuls Mitt Romney, Newt Gingrich and Rick Santorum are touting policies that would push the debt beyond current projections — largely because their proposed tax cuts would outweigh spending cuts. Only Ron Paul’s plans would begin to sharply decrease the debt, according to a report Thursday from the nonpartisan Committee for a Responsible Federal Budget.

The analysis shows how difficult it will be for any president to change the trajectory of the debt. And it underscores the need for bipartisan efforts to increase revenue and curb spending, particularly as an aging population is about to drastically drive up Medicare costs, the group said.

“I don’t think cutting revenues further is the responsible thing to do — and they all do it,” said Alice Rivlin, referring to the Republican candidates. Rivlin, founding director of the nonpartisan Congressional Budget Office, is a director of the watchdog group that released the analysis.

“We’re not going to be able to absorb this tsunami of seniors and their need for health care with the revenue we have,” she said.

Obama’s proposals also would push debt above what budget experts say is sustainable.

The nation’s debt load is typically measured as a portion of the economy, or gross domestic product — with 60 percent being an internationally accepted level of debt. The U.S. so-called public debt, which excludes transfers among government accounts, is about 70 percent of GDP.

Under Obama, the public debt is expected to rise over the decade, to 80 percent of GDP, according to an earlier analysis by the group. It based its projection on his proposals, including ending the George W. Bush-era tax breaks for those earning beyond $250,000 a year.

For its analysis of the GOP candidates, the group compared campaign proposals to existing policies, and those it assumes will occur, including the continuation of the Bush-era tax cuts. Under that baseline, the group said, the debt would reach 85 percent of GDP by 2021.

• Gingrich has noted that the federal budget was balanced when he was House speaker. But the budget group said the policies he’s promoting now would increase the national debt by an additional $7 trillion over the baseline over the next decade to 114 percent of GDP.

• Santorum’s policies would drive up the debt by an additional $4.5 trillion, to 104 percent.

• Romney’s proposals would increase public debt to between 85 percent and 96 percent of GDP, depending on the level of new revenue his proposals could generate in addition to the new tax policies he announced this week, the budget watchdogs said.