WASHINGTON – Discarding their image as the party of obstruction, Republicans opened the new Congress with a flurry of activity designed to put Democrats on the defensive by daring them to oppose efforts to shrink the role of government.

The new Republican House majority is taking the lead in this latest ideological battle between conservatives and liberals that will shape the 2012 campaign. Watching closely from the wings is an influential group of Republican politicians — the party’s presidential contenders, who have effectively ceded control over the issue agenda to lawmakers in Washington.

“That’s extraordinarily unusual,” said Neil Newhouse, a Republican pollster. “Usually, the presidential candidates would set the agenda. In this case, it’s going to be the Congress. They’re playing a much more significant role, simply because we have the majority.”

The new Republican agenda, much of it to be acted on over the next few days and weeks, include House votes to repeal last year’s health care overhaul and sharp cuts — as much as 20 percent — in domestic spending, particularly for social programs and regulatory regimes favored by Democrats.

“The overarching, defining contours of the 2012 campaign are going to be the economy, spending and health care, and what happens in this session of Congress,” said Ralph Reed, a Republican adviser who has yet to sign up with a candidate.

Many of the GOP initiatives, including scrapping the health care law, will die in the Senate, which remains Democratic.

But the votes will have a larger purpose: satisfying the Republican Party’s conservative base and demonstrating to voters nationwide that the new Republican leaders in Congress are heeding “the instructions” of last year’s election to “end business as usual,” as new House Speaker John A. Boehner, R-Ohio, said Wednesday.

The outcome of the new “battle of ideas” that Boehner welcomed in his first speech as speaker could also influence internal Republican politics and what is shaping up as the party’s most wide-open nomination fight in more than 30 years.

Republican presidential candidates are staying out of sight, delaying the start of their announced campaigns and ceding the spotlight to their Washington colleagues.

Likely 2012 contenders were largely absent from the Capitol’s opening-day festivities, and for good reason: None is a prominent congressional figure. That’s a marked departure from recent contests in both parties, when Sens. Bob Dole, John McCain, John Kerry, Hillary Clinton and Barack Obama were leading contenders.

President Obama also ceded the public stage, for the day, to the opposition. Secure in the knowledge that he’ll be renominated, the he will try to pick his fights with a divided Congress.

“The real action is in the House right now. It’s how Boehner takes over as speaker. It’s how Republicans in the House fulfill their campaign promises,” said Scott Reed, who managed Dole’s 1996 campaign (and is no relation to Ralph Reed). “Anybody who would be out trying to compete with what’s going on in the Congress right now would be swimming upstream.”

There are risks in the Republican strategy of launching such a series of confrontational initiatives.

For one, there is a chance that voters may blame Republicans, as they did back in the mid-1990s, if the tug-of-war in Washington degenerates into more partisan stalemate, prompts a government shutdown or temporarily delays an increase in the debt limit, which would reverberate through world financial markets.

The public could also come to regard some of the GOP initiatives as too extreme, particularly as Democrats push back.

Already, Democrats are characterizing the House Republican plan to repeal the health care law as a budget-buster.