Berlin - Pressure is growing on German Chancellor Angela Merkel to show stronger leadership amid eroding popular support for her conservative Christian Democratic Union (CDU).

Three opinion polls released this week showed the CDU losing ground to its centre-left coalition partner, the Social Democrats (SPD), as the economic downturn takes its toll.

With national elections due in the autumn, the unlikely alliance has been hamstrung by what voters perceive as a lack of political will to push through major policy changes.

This has prompted calls from some leading members of the CDU for the party drop its course of seeking to accommodate the SPD and to sharpen its conservative profile.

"It has to be made clear the chapter of the grand coalition has drawn to a close and a new one is opening in which the CDU has to state clearly what it stands for, " said Guenter Oettinger, prime minister of the south-western state of Baden-Wuerttemberg.

Merkel needed to pay more attention to the interests of CDU's business sector and conservative wing, said Oettinger, warning that "no one will take her seriously as a chancellor of compromise."

Wolfgang Bosbach, the CDU floor leader in parliament, said the CDU needed to re-position itself.

"We should never allow ourselves to be viewed as a variant of the SPD. We have to be a clear, political alternative," he told a Cologne newspaper.

Merkel's fortunes and those of her party have waned since the recession took hold in Germany at the end of 2008, and she has been accused of indecision for her slow response to dealing with the crisis.

A Forsa opinion poll saw the CDU slumping to its lowest rating in more than two-and-a-half years - 33 per cent. Another for the ARD television channel showed it down 2 per cent to 32 per cent, while Germany's ZDF television had it dipping 1 per cent to 37 per cent.

In all three polls, the Social Democrats were lagging behind the CDU at between 24-27 per cent, but the gap is closing. For the first time, the ARD poll showed Merkel trailing Foreign Minister Frank-Walter Steinmeier, the SPD candidate for chancellor.

The CDU hopes to win enough votes in the September 27 elections to ditch the SPD and form a new coalition with the smaller, business-oriented Free Democrats (FDP) as junior partner.

Merkel's position has been further undermined by the CDU's Bavarian sister party the Christian Social Union (CSU), whose chairman Horst Seehofer has adopted a combative style since assuming the party leadership in October last year.

Seehofer this week supported SPD moves for higher curbs on executive pay than what the CDU was prepared to agree to. He also called for changes to parts of the recent health reform programme, one of the key reforms of the coalition.

SPD floor leader Peter Struck accused the CSU of being "a factor of instability" in the coalition and said "its lack of trust" in the course taken by the chancellor with the SPD was making it difficult for Merkel to assert herself.

Merkel recently came under fire from conservatives within her party for agreeing to legislation that could result in the nationalization of troubled mortgage lender Hypo Real Estate.

Another test is brewing over demands from struggling carmaker Opel for 3.3 billion euros (4.1 billion dollars) in state aid to help it remain afloat.

"We will provide assistance if the benefits for the people outweigh the losses," said Merkel.

But Deputy Economics Ministry Dagmar Woehrl, a member of the CSU, said it was "highly questionable and unlikely" the government would plough huge sums of taxpayers' money into a company that plans to close plants and lay off thousands of workers. (dpa)