The first sign that the ground had shifted in political fundraising came last year, when conservative groups quickly took advantage of new court rulings to dramatically outspend their liberal rivals.

Now comes the next tremor, as Democratic activists finalize plans for an entirely new political infrastructure in 2012. A network of liberal groups formed in recent weeks is poised to spend $200 million or more in support of President Obama and other Democrats, in large part by raising unlimited donations from wealthy donors.

The effort — spearheaded by a small group of longtime congressional and White House aides — represents Democrats’ response to the electoral drubbing of 2010, when a coterie of conservative and business groups did a far better job than their opponents of adapting to a new campaign finance landscape.

“Our mission is to ensure that when Democrats are attacked by these third-party groups, we are there to respond,” said former Al Gore aide Monica Dixon, the executive director of Majority PAC, a new group that will focus on helping Senate Democrats. “We did not do enough last year to support our candidates. . . . Nobody can sit on the sidelines this year. There’s too much at stake.”

The plans underscore the rapidly growing importance of political groups outside the party system, many of which are free to raise and spend unlimited amounts of money because of a landmark Supreme Court decision and other court rulings last year.

The rulings led to a new kind of political action committee, dubbed “super PACs,” which must disclose their donors to the Federal Election Commission but are not bound by the financial limits that apply to political campaigns. House and Senate candidates are also free to solicit donations on behalf of such groups as long as they do not coordinate with those groups on how the money is spent.

The new Democratic strategy centers on building a network of such groups focused separately on the presidential race, Senate contests and opposition research. Another piece of the puzzle is expected to fall into place this week with the formation of a group to aid Democratic candidates in the House.

The strategy poses a political problem for Obama and other Democrats, who railed against unfettered spending by outside interest groups last year but didn’t pass legislation to curb them. At least two of the new Democratic groups — Majority PAC and American Bridge 21st Century — will include a nonprofit arm that will not have to disclose donors to the public; another group that’s focused on the presidential race could follow the same path.

Chris Harris, a spokesman for American Bridge — which is building a “war room” concentrating on opposition research — compared the situation to a college football coach who still participates in bowl games despite favoring a playoff system.

“In 2010, we sort of sat on our hands in protest and got stomped,” Harris said. “We’ve got to get off the mat and fight back. We may not like the way the system is set up, but we have to work with the system we have.”

Last year, Democrats were particularly critical of American Crossroads, a conservative super PAC, and a nonprofit sister group called Crossroads GPS, which does not have to reveal its donors. The two organizations together raised $71 million from wealthy donors in 2010, and they plan to raise more than $120 million for the 2012 cycle.

“What we’re seeing is a brazen hypocrisy among the center-left and good-government types, who spent enormous amounts of time and resources criticizing” the fundraising tactics of conservative groups in 2010, said American Crossroads spokesman Jonathan Collegio.

In many ways, the emerging Democratic strategy marks a reprise of the 2004 presidential contest, in which several big-money groups helped Sen. John F. Kerry (Mass.).

In 2008, Obama and his team shunned outside groups to consolidate control within the campaign, which raised a record $750 million. For 2012, however, adviser David Axelrod, campaign manager Jim Messina and others have signaled encouragement to independent groups while also setting their own aggressive fundraising benchmarks.

Democratic strategists say they are particularly worried about groups such as American Crossroads — which was formed with the help of GOP political guru Karl Rove — as well as spending by billionaires Charles and David Koch of Koch Industries, who reportedly plan to raise more than $80 million for various conservative projects.

The Democratic-leaning groups announced so far have an assortment of anodyne names: House Majority PAC; Majority PAC, which will focus on the Senate; and American Bridge 21st Century, which had to lengthen its initial title to avoid being confused with a construction firm.

American Bridge was founded by David Brock, a conservative-turned-liberal activist who heads the Media Matters advocacy group. The group will concentrate on gathering and disseminating information about Republican opponents, with a “phase one” budget of about $10 million and room to grow much larger later on, sources said.

Majority PAC — which includes former aides to Gore, Kerry and Senate Majority Leader Harry M. Reid (D-Nev.) — is aimed at closing the gap with conservative groups, which spent almost $50 million more on Senate races in 2010 than their liberal rivals did, according to FEC records.

A fourth major group, not yet named, is likely to be the most influential. Headed by former White House aides Bill Burton and Sean Sweeney, the organization will focus on aiding Obama in the presidential race and could include both a super PAC and a nonprofit akin to the American Crossroads model, strategists said. The group hopes to spend at least $100 million — and probably much more than that — in an attempt to keep up with conservative organizations, sources said.

Unlike in 2004, when outside groups ran most get-out-the-vote operations, Democrats say the Obama campaign will spend much of its money trying to reestablish the “ground game” that helped inspire historic turnouts among blacks and voters younger than 30 last time. Pro-Democratic labor unions are also expected to mount aggressive organizing efforts in states such as Wisconsin, where GOP governors have taken on public employees.

“The negative results in November were a pretty significant wake-up call,” said one top Democratic adviser, who spoke on the condition of anonymity to discuss details of the effort. “Sometimes people respond better to a crisis than they do to an early warning system.”

Staff writers Perry Bacon Jr. and T.W. Farnam contributed to this report.