Voters in Germany's most populous state inflicted an embarrassingly heavy defeat on Chancellor Angela Merkel's conservatives Sunday and strengthened a regional government that the German leader's party had portrayed as irresponsibly spendthrift.

The outcome boosted Germany's center-left opposition, and was a bitter pill to swallow for Merkel's Christian Democrats as the country looks toward national elections due late next year and the chancellor grapples with Europe's stubbornly persistent debt crisis.

The center-left Social Democrats and Greens — Germany's main opposition parties — won combined support of 50.4 percent in the election in North Rhine-Westphalia. That gave them a majority in the state legislature, which they narrowly missed in the last regional election two years ago.

Meanwhile, support for Merkel's party plunged to 26.3 percent from 34.6 percent in 2010, its worst showing in the state since World War II.

"The likelihood has become significantly greater that the next chancellor will be a Social Democrat," the opposition party's general secretary, Andrea Nahles, proclaimed on ARD television.

Still, the pro-market Free Democrats, Merkel's struggling partners in the national government, performed respectably, polling 8.6 percent — a result that may help stabilize the party.

The state government of popular Social Democratic governor Hannelore Kraft had been favored to win, particularly after a much-criticized and gaffe-prone campaign by conservative challenger Norbert Roettgen, Merkel's federal environment minister.

Even so, senior conservative lawmaker Peter Altmaier said that "this result exceeds our worst fears."

"This is a crashing defeat for Mrs. Merkel and her minister," Nahles said. The Social Democrats' share of the vote climbed to 39.1 percent from 34.5 percent.

"The defeat is bitter, it is clear and it really hurts," Roettgen said minutes after polls closed, announcing that he would give up the leadership of the Christian Democrats' local branch. "This is, above all, my personal defeat."

About 13.2 million people were eligible to vote in the western state, a traditional center-left stronghold that includes Cologne, Duesseldorf and the industrial Ruhr region. Turnout was barely changed at 59.6 percent.

North Rhine-Westphalia voted three years early after Kraft's incumbent minority government failed to get a budget passed in March. Merkel said then that the election offered the region an opportunity to choose a government that wouldn't take on "ever more debt."

While national polls show Germans support Merkel's pro-austerity stance in Europe, prominent Christian Democrat Peter Hintze said voters in North Rhine-Westphalia viewed regional budget deficits as an "abstract theme."

Roettgen faced criticism for not committing himself to stay in state-level politics and for saying, in an apparent attempt at irony, that "regrettably" voters rather than his party would decide whether he became governor.

He irritated his party by declaring Sunday's election would decide "whether Angela Merkel's course in Europe is strengthened or whether it is weakened by the re-election of a pro-debt government in Germany." Merkel said it was an important state election, "no more and no less."

The Free Democrats, often blamed for frequent infighting in Merkel's government, can build on a surprisingly strong performance last weekend in the northern state of Schleswig-Holstein after several miserable results over the past year.

The party, which also picked debt as an election issue, appeared to have done better than the conservatives at mobilizing center-right voters. Their national leader, Vice Chancellor Philipp Roesler, declared that "people are listening to us again and they trust us."

The upstart Pirate Party, which has surged lately with a platform of near-total transparency and Internet freedom but lacks policies on many issues — including the debt crisis — entered its fourth state legislature with support of 7.8 percent.

Voters gave the hard-left Left Party, which thrived as a voice of protest over recent years, just 2.5 percent, ejecting it from the local Parliament.

Sunday's election came a week after Schleswig-Holstein voted out a center-right coalition made up of the same parties as the national government, but failed to hand the main opposition parties a majority.

It also followed setbacks for Merkel's austerity-led response to the eurozone debt crisis in French and Greek elections.

Sunday's election — unlike North Rhine-Westphalia's last vote in 2010 — won't change the national balance of power.

Two years ago, Merkel's coalition lost the state after five years in power there. That erased the national government's majority in the upper house of Parliament, which represents Germany's 16 states, and its position there has since weakened further.

In the lower house, Merkel needs the emboldened Social Democrats' support to win a two-thirds majority for the European budget-discipline pact she has pushed. They have yet to specify their price though they have called for a tax on financial transactions.

Nahles said the party — which has backed rescue plans so far — would continue to be "responsible on European policy."

Merkel's own popularity ratings remain high and current national polls show her conservatives as the biggest party. However, they forecast a parliamentary majority neither for her center-right coalition nor for the Social Democrats and Greens, who ran Germany from 1998 to 2005.

That suggests that Merkel can hope to hold on to power when the national election comes, though perhaps with a new coalition partner.