SPD secures enough votes on coalition deal to ensure its validity BERLIN (Reuters) - More than one in three members of Germany's center-left Social Democrats (SPD) has already voted on a proposed coalition deal with Chancellor Angela Merkel's conservatives, ensuring the internal party referendum will be valid. Merkel easily won an election in September, but came up just short of a parliamentary majority, forcing her to find a coalition partner. After a month of talks with the SPD, the two camps clinched a coalition agreement that includes a 185-page policy blueprint for a new government. But due to deep reservations within the SPD rank-and-file about entering another coalition with the conservatives, SPD leaders agreed to put the deal to a vote of their 474,000 members. For the vote to be valid, 20 percent of SPD members needed to participate. Results are due by December 15. Almost 200,000 members had submitted their postal ballot by Friday lunch time, according to a letter by SPD General Secretary Andrea Nahles seen by Reuters on Friday, easily beating the participation rate needed to make the vote count. SPD members are widely expected to approve the deal despite reservations. On Friday, several SPD luminaries, including former Chancellors Helmut Schmidt and Gerhard Schroeder, urged the party to back a "grand coalition," publishing a one-page ad in mass-daily Bild entitled "responsibility for Germany and Europe." The SPD won policy compromises from the conservatives in some important areas such as a nationwide minimum wage, investment in education and infrastructure and relaxed rules on dual citizenship but had to cede ground on other policies. Clearing another potential hurdle, Germany's Constitutional Court in Karlsruhe on Friday rejected an injunction seeking to stop the SPD ballot on the grounds that it was unconstitutional to give SPD members more say than other voters. Reporting by Holger Hansen and Annika Breidthardt; Editing by Noah Barkin