By Andreas Rinke and Bettina Borgfeld
BERLIN/GREIFSWALD, Germany (Reuters) - German Chancellor Angela Merkel, poised to win a fourth term in Sunday's election, and her center-left challenger Martin Schulz urged supporters on Saturday to keep fighting for votes with a third of the electorate still undecided.
Merkel is widely expected to cruise to re-election with the Schulz's Social Democrats trailing by double digits but the far-right Alternative for Germany (AfD) could emerge as the third largest party, complicating the outlook for her next coalition.
A new INSA poll published by Bild newspaper showed sliding support for Merkel's conservatives, who dropped two percentage points to 34 percent, and the SPD, down one point to 21 percent - both now joined in an unwieldy "grand coalition".
The anti-immigrant AfD, meanwhile, rose two percentage points to 13 percent, cementing its bid to be the first far-right party to enter parliament since the end of World War Two.
Merkel urged supporters to drum up votes by focusing on conservatives' efforts on behalf of families, a pledge to avoid tax increases and emphasis on increasing security in Germany.
The Christian Democratic leader also lauded the role of the European Union in providing stability in "a troubled world".
"We want to boost your motivation so that we can still reach many, many people today. Many are still undecided," Merkel said before heading north to her home constituency.
In Greifswald, she led a crowd in practicing CPR as loudspeakers blared the Bee Gees song "Stayin' Alive".
"I should be in better shape, with the international media here, but I'll give it a try," a smiling Merkel told the crowd.
First elected in 2005, Merkel remains popular in Germany but has regularly faced jeers and whistles from left- and right-wing demonstrators during rallies during this campaign.
In Munich on Friday, Merkel defended her 2015 decision to admit about one million asylum seekers on humanitarian grounds, but pledged to prevent a repeat of that crisis.
In the western city of Aachen, Schulz pledged to fight for every vote until polls close at 6 p.m. on Sunday. He said high voter turnout was vital to offset growing support for the AfD, whom he described as "a party of haters."
"Young people, think about Brexit. Think about Trump," he said. "Go vote. Take this right to vote seriously, and use it."
Schulz said the SPD overcame resistance from conservatives in their coalition to push through a minimum wage, same-sex marriage and other social priorities.
Schulz asserted that Merkel was "a world champion in not deciding," someone who simply parroted others' ideas.
He vowed to push for further reforms, including better elderly care facilities, affordable housing, an end to discriminatory practices that harm children of migrants, and free child care.
MOUNTING CONCERN ABOUT AfD
Merkel's interior minister, Thomas de Maiziere, told Internet provider t-online.de the government would combat "Islamist terrorism" by strengthening European borders and bolstering security at home.
He criticized the AfD as "a wolf in sheep's clothing" and said Germany's BfV domestic intelligence agency was studying "whether right-wing extremists are seizing power and exerting influence on the party".
The AfD was founded in 2013 with the original goal of opposing large bailouts of financially strapped euro zone countries but from 2015 shifted its focus to immigration.
Mainstream parties have ruled out governing with the AfD.
It has come under increased scrutiny in recent weeks after its top candidate Alexander Gauland said the German integration minister should be dumped in her parents' homeland of Turkey, and that Germans should be proud of what their military did in World War One and Two.
Jewish and Muslim groups say the AfD's rhetoric has opened the door to more hate speech and anti-Semitism.
Josef Schuster, president of the Central Council of Jews in Germany, told Reuters he feared the AfD's entry into parliament would change the public tone in Germany. "I worry that the AfD will aggressively deepen divisions in our country," he said.
The AfD, which has already won seats in 13 of 16 state legislatures in Germany, has promised to reenergize debate in the federal parliament after four years of what it calls "boring" rule by Merkel's grand coalition.
AfD executive board member Georg Pazderski told Reuters the party was seeing a huge increase in support. "People are no longer ashamed to come to the AfD and to identify with the AfD."
Electoral arithmetic might yet nudge Merkel to renew her coalition with the SPD, or she might opt for a three-way alliance with the pro-business Free Democrats (FDP) and environmental Greens.
FDP Chief Christian Lindner told a rally in Duesseldorf his party hoped to be the third biggest force in parliament, but would only govern if its demands and conditions were met.
"We won't govern at any price," he said, suggesting the FDP could potentially have more impact as an opposition force.
(Additional reporting by Andrea Shalal, Gernot Heller and Reuters TV; editing by Mark Heinrich)