German Chancellor Angela Merkel of the Christian Democrats (CDU) and Social Democrat (SPD) challenger Frank-Walter Steinmeier are to step in front of the cameras for a televised debate on Sunday, two weeks before the general election, according to dpa. The live 90-minute TV duel, broadcast during prime viewing time on four channels, is the only occasion when Merkel and Steinmeier meet head-on to debate election pledges, before the September 27 poll. High viewer ratings were anticipated for the debate, which 54 per cent of respondents said they would probably watch, in a survey conducted for German Bild am Sonntag newspaper. The SPD, trailing badly in the polls, hoped that Steinmeier's appearance would win over undecided voters. "(Steinmeier) will convince the people - of his substance, his goals, his person," SPD Chairman Franz Muentefering told German daily Tagesspiegel. The opposition Free Democrats (FDP) criticized the format of the debate in which Merkel and Steinmeier, partners of four years in the ruling CDU-SPD grand coalition, attack each other's style of government. "It is unacceptable, undemocratic and unfair," FDP Chairman Guido Westerwelle told Bild am Sonntag, adding that the opposition should be invited to challenge the government instead. The debate could be a turning point in Germany's lacklustre election campaign, as the required majority for Merkel's preferred CDU-FDP coalition has begun to look less certain. Latest opinion polls give CDU 36 per cent of the vote, and 14 per cent for the FDP, bringing the two parties - who have said they would like to form a government together - to a joint 50 per cent. The SPD has been unable to budge its approval beyond the low 20s, with current ratings at 23 per cent. A so-called "traffic light" combination of SPD (red), FDP (yellow) and Greens could garner 48 per cent of the vote, according to the latest survey commissioned by German ZDF state television. A renewal of the CDU-SPD grand coalition - unloved by both partners - would still capture the largest share of the voters, with a combined 59 per cent. Many viewers may still vote with their remote controls during Sunday's debate, as television channel Pro 7 is screening The Simpsons Movie to coincide with Merkel and Steinmeier's confrontation. September 13 , SPA --