BERLIN (Reuters) - Germany's Social Democrats (SPD) saw their lead over Chancellor Angela Merkel's conservatives narrow in a poll published on Tuesday, pointing to a tightening race just five days before a federal election.

       The SPD, whose candidate for chancellor Olaf Scholz is currently vice chancellor and finance minister in Merkel's grand coalition, remained stable at 25%, according to the Forsa poll for RTL/n-tv television.

       Support for the conservative CDU/CSU alliance, whose chancellor candidate is Armin Laschet, edged up one percentage point to 22%.

       The other parties were all unchanged with the Greens on 17%, the business-friendly Free Democrats (FDP) at 11%, the far-right AfD at 11% and the anti-capitalist Left party at 6%.

       Forsa projected that the SPD would win 206 seats in the next Bundestag, the lower house of parliament, the CDU/CSU bloc 185, the Greens 140, the FDP and the AfD both 91 each and the Left 49.

       This raises the possibility of four coalition options after Sunday's election:

       - the SPD with the Greens and FDP, also known as a traffic light coalition due to their party colours of red, green and yellow;

       - the CDU/CSU bloc with the Greens and the FDP, described as a Jamaica coalition in reference to the country's flag and the party colours of black, green and yellow;

       - SPD with the Greens and the Left, dubbed R2G or red-green-red coalition;

       - or an SPD-led grand coalition with the conservatives as junior partner.

       All parties have ruled out working with the populist, far-right AfD.

       Scholz and the Greens have also poured cold water on the idea of forming a coalition with the conservatives, saying that the CDU/CSU alliance needed to rebuild itself in opposition following 16 years of Merkel's consensus-driven, centrist rule.

       (Reporting by Michael Nienaber, editing by Giles Elgood)