BERLIN: Germany's vice chancellor is struggling to quell speculation about his leadership of the country's junior governing party, whose dire poll ratings are a complicating factor as Chancellor Angela Merkel seeks re-election this year.

Philipp Roesler, who is also Germany's economy minister, appealed to his pro-market Free Democratic Party on Sunday to show unity ahead of a state election in his home region of Lower Saxony on Jan. 20, an important political test ahead of national elections in September.

Polls suggest the center-left opposition has a good chance of winning Lower Saxony from Merkel's center-right alliance, largely because the FDP is very weak, and claiming a significant boost ahead of the national vote.

Speaking at a traditional New Year party rally in Stuttgart, Roesler portrayed his party - which opposes government intervention in the economy - as the only one which defends traditional German economic principles. The FDP is, he said, "the economic policy corrective in this government."

The party has often talked particularly tough on the eurozone debt crisis, and Roesler stressed anew its vehement opposition to pooling European countries' debt.

The FDP became Merkel's junior governing partner when it won nearly 15 percent of the vote in Germany's 2009 election with a campaign that focused heavily on substantial tax cuts. It failed to achieve them and received much of the blame for frequent squabbling in the coalition; it currently polls just below the 5 percent needed to win parliamentary seats both nationally and in Lower Saxony.

Roesler became party leader and vice chancellor in May 2011, when he declared that "starting today, the FDP will deliver."

That has haunted him as the party flatlined in polls, while Merkel's conservative Christian Democrats are strong and the chancellor is fortified by her handling of the debt crisis and a strong economy. Merkel's center-right coalition lacks a majority in national polls, but they suggest she may well be able to keep power after September by seeking a new partner.

Speculation has swirled for months that Roesler, 39, would have to go if the FDP does badly in Lower Saxony, and carping from members has intensified recently. Development Minister Dirk Niebel vented his frustration about the situation in a speech to Sunday's event, insisting that the party can't wait until a scheduled convention in May to choose its election campaign team.

"Things can't carry on in the FDP as they are now," he said. "It tears me up inside when I see the state of my, our FDP."

Roesler said that credibility is "also a question of style, fairness and solidarity." He urged the party to "send a signal that we are ready to fight together" in Germany's election year.