WASHINGTON — The congressional battle over health care entered a new, more sharply partisan phase this week, as Republicans began building a case for dismantling the law while Democrats and President Obama fought back hard.

And though Obama said Friday he’d consider a “tweak” or two, he also sent strong signals he won’t accept major changes.

GOP lawmakers pressed their points at the first hearings of the new 112th Congress, and Friday, Obama answered with a rousing defense of the 10-month-old law.

“You may have heard once or twice that this is a job-crushing, granny-threatening, budget-busting monstrosity,” he told Families USA, a consumer-oriented health care group that gave him an enthusiastic reception.

“That’s about how it’s been portrayed by opponents. And that just doesn’t match up to the reality,” he said.

Obama’s blunt rhetoric came three days after his calmer tone in his State of the Union address. In that speech, he said of health care, “So instead of re-fighting the battles of the last two years, let’s fix what needs fixing and move forward.”

But the partisan war has been escalating on Capitol Hill, and shortly after Obama spoke Friday, Republican Senate leader Mitch McConnell of Kentucky fired back.

“We need to repeal this bill and replace it with common-sense reforms that will actually lower costs, prevent unsustainable entitlement promises and make it easier for employers to start hiring again,” he said.

The exchange indicates that the health care battle is likely to rage for some time, and while the odds of a GOP legislative success remain slim, Democrats remain concerned the GOP can lure enough votes to change or end less popular parts of the act.

Last week, the House of Representatives passed, on a largely party-line vote, a repeal of the entire law. The Senate is expected to vote soon. Since Democrats control 53 of the Senate’s 100 seats, and it would take two-thirds majorities of each House to override an Obama veto, the effort is going nowhere.

That’s one reason Republicans, who control the House, are looking at pieces of the law. Committees began hearings this week, and at the House Budget Committee, Chairman Paul Ryan, R-Wis., put the choices in stark terms.

“We face a choice of two futures,” Ryan said. “And nowhere in this country is this choice more clearly defined as it is in health care. Down one path lies a dramatic decline of a government-run system on the verge of bankruptcy. There is an alternative path.”

With the Democrats’ strength in numbers, even getting piecemeal changes adopted will be tough.

Republicans’ biggest target is the individual mandate, which requires most people to have coverage by 2014 or face penalties. Chances are, that issue will be decided by the courts, since more than half the states are challenging its constitutionality.

In the meantime, conservatives are eager to deny funds the new law needs to work. The nonpartisan Congressional Budget Office figures that government agencies will need $10 billion to $20 billion over the next 10 years.