Germany's opposition Greens party, with solid chances of returning to power after the next federal election in 2013, decided at a weekend party congress to push for higher taxes on the rich and eliminate some corporate tax breaks.

The Greens have been riding high in opinion polls and could be well-positioned to form a coalition with their preferred partners, the centre-left Social Democrats (SPD), or Chancellor Angela Merkel's conservatives (CDU/CSU).

But the Greens have been adrift since the spring after Merkel's centre-right coalition robbed them of their signature issue by agreeing to shut the country's nuclear power plants by 2022. The Greens had led the anti-nuclear movement for decades.

The 800 delegates to the party congress in the northern city of Kiel drafted a programme to raise taxes on the rich and companies as a remedy for the sovereign debt crisis. Higher taxes on the rich are likely to strike a chord with most voters.

They agreed to push for raising the top income tax bracket from 42 percent to 49 percent for those earning 80,000 euros a year or more, and a wealth tax on all those with assets of more than 1 million euros. Some wanted the top rate raised to 53 percent but failed to win a majority.

The Greens called to eliminate tax breaks on company cars, remove many corporate energy tax breaks and end tax breaks for married couples -- a batch of left-leaning proposals that would make it hard to find common ground with the conservatives.

Stronger shoulders have to carry the weight that those with weaker shoulders can't, said Juergen Trittin, parliamentary floor leader for the Greens and leading voice of the left who is reportedly interested in becoming Finance Minister in 2013.

Greens co-chair Cem Oezdemir, a leader of the party's pragmatic wing, warned against viewing industry as the enemy. And Winfried Kretschmann, the Greens' state premier of Baden-Wuerttemberg, urged the party against overburdening companies.

We don't want an orgy of tax increases, said Kretschmann, who made history in March by becoming the first Greens politician to be elected to lead one of Germany's 16 states. We've got to watch out that we don't overdo it.

Opinion polls show a majority of Germans want higher taxes, especially on high wage earners. The public has high expectations on the state and public sector services.

The Greens were in power with the SPD from 1998 to 2005, a government that lowered taxes on top wage earners.

The Greens would win about 14 percent of the vote if an election were held now, according to a representative opinion poll published on Thursday by Forsa for Stern magazine. That is down from a high of 28 percent in the spring when nuclear fears were running high in the wake of the Japanese disaster.

They are still the third largest political force in Germany behind Merkel's CDU/CSU (36 percent) and the SPD (26 percent). Merkel's FDP partners are at 3 percent and would fail to clear the 5 percent threshold needed for seats in parliament.

Drawing considerable media attention on Sunday was the Greens' desire to eliminate plastic shopping bags by introducing a punitive tax -- and if the fee fails to curb the use of shopping bags they should then be outlawed altogether.

(Writing by Erik Kirschbaum; Editing by Peter Graff)