By Geir MoulsonBERLIN -- She enjoys overwhelming popularity and leads an economy that's the envy of Europe. Angela Merkel, however, is in a fight to clinch a new term for her ruling coalition in Sunday's national election -- with polls showing her center-right alliance on a knife edge as her junior partner's support slumps. Merkel and her conservative Christian Democratic Union appear likely to fend off a challenge from center-left rival Peer Steinbrueck and emerge as the biggest party in parliament's lower house, whose members choose the chancellor -- making her the strong favorite to win a third term. But no single party has won an absolute majority in Germany in more than 50 years. Surveys show that Merkel's coalition partner, the pro-business Free Democratic Party, has fallen from the nearly 15% support it won in 2009 to about the 5% needed to keep any seats in Parliament. If Merkel's alliance falls short of a parliamentary majority, the most likely outcome is a switch to a Merkel-led "grand coalition" of her conservatives with Steinbrueck's Social Democratic Party -- the same combination of traditional rivals that ran Germany from 2005-2009 in Merkel's first term. That's unlikely to produce a radical change in policies. However, it could signal a subtle shift in emphasizing economic growth over the austerity that Germany has insisted on in exchange for bailing out economically weak European countries such as Greece. Final results are due within hours of polls closing. However, with margins so close, the country could still face weeks of horse-trading before a clear picture emerges about the makeup and policies of Germany's next government. Merkel's center-right coalition might win re-election but "it will be very tight," said Oskar Niedermayer, a political science professor at Berlin's Free University. Much may depend on the turnout among the nearly 62 million voters -- about 70% four years ago. Political leaders fought Saturday to mobilize their supporters and win over the undecided. "I'm personally asking people in Germany to give me a strong mandate so that I can serve Germany for another four years, make policies for ... a strong Germany, for a country that is respected in Europe, that works for Europe; a country that stands up for its interests in the world but is a friend of many nations," Merkel said at a rally in Berlin.