By Paul Carrel
BERLIN (Reuters) - Germans vote in three regional state elections on Sunday, with Chancellor Angela Merkel's conservatives at risk of setbacks that would weaken her just as she tries to push through a deal to resolve Europe's migrant crisis.
Migration is the hot topic, as worry how Germany will cope with an influx, totaling more than a million last year alone, that has come to define Merkel's leadership, and on which she has staked her reputation.
Merkel's conservative Christian Democrats (CDU) have been losing support to the anti-immigration Alternative for Germany (AfD) party, which has profited from the growing unease.
Asked at a campaign rally on Saturday how she was preparing for Sunday's results, Merkel said: "I'm crossing my fingers."
Polls indicate that the CDU will remain the biggest party in Saxony-Anhalt, in former East Germany. In the west, it could be pipped by the Greens in Baden-Wuerttemberg, where it is currently the largest party. And in Rhineland-Palatinate, where the CDU came a close second last time, the race is too close to call.
A failure to win at least two of the three states would be a blow for Merkel just as she is trying to use her status as Europe's most powerful leader to push through an EU deal with Turkey to stem the tide of migrants.
The chancellor alarmed many European leaders at a summit earlier this week by gambling on the last-minute draft deal with Turkey to stop the migrant flow, and demanding their support.
Merkel still needs to seal the deal at another summit on March 17-18. If her party performs poorly on Sunday, she will go into that meeting weakened.
One of those draining support from Merkel's CDU is the AfD.
Already represented in five of Germany's 16 regional parliaments, the anti-immigration party looks set to burst into three more on Sunday, campaigning on slogans such as "Secure the borders" and "Stop the asylum chaos".
Polls put the AfD's support as high as 19 percent in Saxony-Anhalt, where the CDU and Social Democrats now govern in a 'grand coalition' that mirrors Merkel's federal government.
If the AfD performs as well as the polls indicate, the coalition partners may need to team up with a third party to assemble a majority - one of a number of potential 'firsts' for German politics as voter loyalties splinter.
(Editing by Kevin Liffey)