Chancellor Gerhard Schroeder underlined that he will not form an alliance with the new Left Party and dismissed speculation over other possible coalitions.
Buoyed by polls this month that have shown his party clawing back support, Schroeder said his aim was "for the Social Democrats to be the strongest party."
"The trend is upward," the chancellor was quoted as telling the daily Passauer Neue Presse. "There is a lot of movement in the polls."
Recent surveys have raised doubts over whether conservative challenger Angela Merkel's Christian Democrats will be able to form her preferred center-right coalition with the pro-business Free Democrats _ prompting speculation she may have to turn to Schroeder's party to form a so-called "grand coalition."
Merkel still appears likely to emerge as chancellor. But recent polls have raised the possibility that an alliance of Schroeder's current coalition _ the Social Democrats and Greens _ with the Left Party, a combination of ex-communists and former Social Democrats alienated by the chancellor's welfare state reforms, could garner enough support to rule together.
Still, all three parties have dismissed the idea of forming a three-way coalition, which would face major policy and personality clashes.
"Such a coalition is completely out of the question," Schroeder said, adding that "there will no form of collaboration" with the new party.
Schroeder also dismissed talk of other possible permutations, among them a combination of Social Democrats, Greens and Free Democrats, the AP reports.