By Madeline Chambers and Holger Hansen
BERLIN (Reuters) - The leader of Germany's Social Democrats (SPD) will put forward Martin Schulz, the former president of the European Parliament, to challenge conservative Chancellor Angela Merkel in a national election on September 24, sources said on Tuesday.
Sigmar Gabriel's decision, reported by Stern magazine and confirmed by party sources, will make Germany's election less predictable and also signals the SPD wants to end its role as junior partner in Merkel's current right-left coalition.
Opinion polls suggest Schulz has a better chance than Gabriel of unseating Merkel, who has led Germany since 2005 and is Europe's most powerful leader. Her conservatives' coalition with the SPD has governed Germany since 2013.
"If I were to stand, I would fail and the SPD would fail with me," Gabriel, who serves as vice chancellor and economy minister in Merkel's government, told Stern magazine.
"All the polls have shown that people don't want a grand coalition any more. In people's minds I stand for that. So Martin Schulz is the most suitable man," one person at the party meeting quoted Gabriel as saying.
The party is expected to formally decide on Schulz's candidacy for chancellor in the near future. If confirmed, he faces a very tough job beating Merkel, whose conservatives lead in opinion polls by about 15 percentage points.
But a poll conducted this month by the Emnid institute for the Bild newspaper showed that in a direct vote Schulz would win 38 percent versus 39 percent for Merkel, compared to a result of 27 percent for Gabriel and 46 percent for Merkel.
The SPD aims to form a coalition with smaller parties on the left but most analysts still think another right-left coalition is the most likely outcome of September's election.
Schulz, 61, said in November he would return to German politics after his stint as president of the European Parliament.
Stern reported that Gabriel, 57, a former schoolteacher, would also offer to give up his chairmanship of the SPD, a position he has held since 2009. Gabriel is the longest serving leader of the SPD since former Chancellor Willy Brandt.
German weekly Die Zeit, citing no sources, reported that Gabriel would seek the post of foreign minister.
The role of foreign minister will become available soon as Frank-Walter Steinmeier, also a leading member of the SPD, is expected to be elected to the largely ceremonial role of German president next month.
(Reporting by Klaus Lauer, Holger Hansen, Joseph Nasr, Andrea Shalal, and Michelle Martin; Writing by Madeline Chambers; Editing by Gareth Jones)