WASHINGTON — Mitt Romney is adamant: “I will press for full repeal of Obamacare, which will save hundreds of billions of dollars.”

But the nonpartisan Congressional Budget Office — whose data the campaign has cited as the source of its assertion — says the 2010 federal health-care law should cut deficits $210 billion from 2012 to 2021.

The bottom line: “It’s actually not known who’s right,” said Amitabh Chandra, economist and professor of public policy at Harvard University.

“If the law goes through as it is, it will save us money,” he said. But what if Washington lawmakers — as they often do — balk at implementing some of the cost-savings features, such as higher taxes or significant cuts in Medicare?

There go the big savings.

“Congress has a history of doing things like that,” Chandra said.

The CBO

The quandary over deciding who’s right is typical when trying to evaluate campaign assertions. It’s difficult to say whether Romney is accurate or exaggerating, although some analysts said that, at the least, he’s using CBO’s analysis selectively.

The agency is widely regarded as Capitol Hill’s leading independent authority on the fiscal impact of legislation, and its reviews can only deal with current law.

“CBO estimates are always credible because of the organization’s reputation for technical skill and lack of bias,” said Paul Ginsburg, president of the nonpartisan Center for Studying Health System Change.

“CBO has studied this a lot more than Romney has, so I’ll go with CBO,” said Augustine Faucher, director of macroeconomics at Moody’s Analytics, a West Chester, Pa.-based research firm.

The accuracy of the CBO’s numbers “depends on whether you want to reduce the deficit on paper or in reality,” said Kathryn Nix, health care policy analyst for the conservative Heritage Foundation.

“Think about the assumptions that go into that (the CBO) study and what’s likely to happen in real life. This law is going to explode the deficit.”

A key issue

Romney, the former Massachusetts governor considered a front-runner for the Republican presidential nomination, made his assertion in a Sept. 29 op-ed article in the New Hampshire Union Leader.

Romney has made repealing the 2010 health-care law, which would require nearly everyone to obtain health coverage by 2014, a centerpiece of his presidential campaign.

His opposition to the law, which most Republicans abhor because they see it as big government run amok, is an important talking point for Romney, since as governor of Massachusetts he signed into law a state health-care plan widely considered a model for the federal law.