BERLIN (Reuters) - The head of Angela Merkel's allies in Bavaria has attacked a plan by the opposition Social Democrats (SPD) to put any decision on forming a "grand coalition" with her to a vote of its members, warning against tactics that risk stability. The SPD decided late on Friday it would poll its 472,000 grassroots members if it ends up deciding to join Merkel, a union many in the party oppose, in what could be an unwieldy process that could complicate the creation of a new government. Bavaria State Premier Horst Seehofer said Germans had expressed the wish in last Sunday's ballot for a government led by Merkel, and to torpedo attempts to create a coalition on tactical grounds would damage the politics and the SPD itself. Germany should aim for a new coalition within the next two months, he said, otherwise it risked making itself look ridiculous in the eyes of the world. Her conservatives need a new coalition partner and would prefer a grand coalition with the SPD, a reprisal of the right-center alliance she led from 2005 to 2009. But SPD leaders and party members fear a loss of identity. In an extraordinary meeting on Friday 200 SPD leaders gave embattled chairman Sigmar Gabriel a green light to begin exploratory talks with the conservatives to see if there is scope for full-fledged talks. Ordinarily a party chairman or a small group makes decisions to enter talks but Gabriel, under pressure for another election drubbing, is being cautious and seeking party endorsements for all key decisions. According to the decision on Friday, all 472,000 SPD members would be given the chance to vote on any decision to form a grand coalition in mid-November, before the annual SPD party congress in Leipzig set for November 14-16. An opinion poll on Friday showed two-thirds of SPD members oppose a grand coalition because they fear the party could wither further in the shadow of the popular chancellor.