Berlin  - Chancellor Angela Merkel could struggle to win enough backing for her preferred coalition of her conservatives and the Free Democrats (FDP) at this week's German election, according to opinion polls released Wednesday.

Two polls showed a total 1- or 2-point lead for Merkel's Christian Democrats (CDU) and the FDP, who were predicted a combined 48-48.5 per cent of the vote in Sunday's general election.

The same surveys - by pollsters Forsa and Allensbach - said a total of 46.5-47 per cent would vote for the Social Democrats (SPD), Greens or the Left Party.

A third poll, released by Berlin-based Info GmbH, showed a contrary result, giving CDU-FDP just 46 per cent, while Social Democarts (SPD), Greens and Left could jointly expect 49 per cent of the vote.

While the SPD has ruled out entering into government with the Left Party, the CDU and FDP could not form a feasible coalition without an overall parliamentary majority.

The likely alternative to a CDU-FDP government would therefore be a renewal of the current, uneasy "grand coalition" between CDU and SPD.

Merkel's popularity has also fallen according to Forsa.

Asked who they would pick as chancellor, 35 per cent chose Merkel - down two points on last week's figures, which came after she gave a disappointing TV performance opposite her SPD challenger, Frank-Walter Steinmeier.

Steinmeier saw his approval ratings increase by two points, to 26 per cent. Germans do not vote directly for their chancellor, who is appointed by the political parties.

The CDU's deputy leader Roland Koch appealed for his party to engage more in the final days of the election campaign.

"Nobody should think that we can win the parliamentary election from the spectators' stand," Koch told German daily Hamburger Abendblatt.

Koch, who is also state premier of Hesse, defended Merkel's low-key approach to the election campaign, which he said was appropriate during the economic crisis.

"However, we also need the engagement to jointly convince every single voter," Koch added.

Forsa and Allensbach, both showed 35-per-cent approval ratings for the CDU, 24-26 per cent for the SPD, 13-13.5 per cent for FDP, 11 per cent for the Greens and 10-11.5 per cent for the Left Party.

The surveys questioned between 1,200 and 2,500 people. (dpa)