By Alastair Macdonald and Philip Blenkinsop
BRUSSELS (Reuters) - European Parliament President Martin Schulz is returning to German politics, raising the prospect he may challenge Angela Merkel as chancellor and prompting speculation of a reshuffle in European Union institutions.
Schulz, a Social Democrat, told a news conference he would not stand for re-election as speaker of the EU legislature and instead campaign for a parliamentary seat in Berlin next year.
He made no comment on speculation he may succeed departing German Foreign Minister Frank-Walter Steinmeier or become the Social Democrat SPD's candidate to challenge the conservative Merkel's bid for a fourth term as chancellor in September's parliamentary election.
Schulz, 60, had been pushing for a third 30-month term as EU parliament president in defiance of a deal that he make way for a speaker from the centre-right, the chamber's biggest group.
Should the conservatives, who have formed an effective grand coalition in Brussels with Schulz's centre-left, claim the presidency in January, all three main EU political bodies would be headed by the centre-right -- a possibility that has raised talk of change at the European Commission and European Council.
Commission President Jean-Claude Juncker had pressed his fellow conservatives in Parliament to let Schulz stay on in the interests of stability following Britain's vote in June to leave the bloc. He denied earlier this week that he had threatened to resign himself if Schulz were forced out.
Luxemburger Juncker, who said on Thursday he regretted Schulz's departure, has a five-year mandate running until October 2019. Council President Donald Tusk, the former Polish prime minister who will chair Brexit negotiations, has a 30-month mandate that expires in May.
He has broad support among member governments to stay on -- though not from his home country, where his opponents are now in power. He has not publicly stated whether he plans to continue.
CONSERVATIVE AMBITIONS
The conservative leader in Parliament, Manfred Weber from Merkel's Bavarian Christian Social Union allies, told a news conference after Schulz's announcement that his group would choose a candidate for speaker next month.
Weber, 44, has been cited as a successor himself, a move which could sharply raise his profile for a future career in Germany -- something Schulz also used to his advantage.
Weber did not, however, rule out that his group might back a "consensus candidate" from another of the mainstream, pro-EU blocs in the chamber, which include liberals and greens. That could dampen complaints of a centre-right lock on institutions while, as Weber said, maintaining a centrist front against the chamber's vocal minority of eurosceptic and extremist parties.
Speculation that Schulz would return to German politics grew after Merkel's grand coalition government with the SPD backed Schulz's party ally Steinmeier to take over in February as Germany's figurehead president. German media have tipped Schulz as Steinmeier's successor as foreign minister.
Whoever takes over the role will have an overflowing in-tray as Germany tries to unite a divided post-Brexit EU, contain an assertive Russia and work out a new relationship with Washington under Donald Trump. Schulz has said Trump's election as president will make work harder for the European Union.
Opinion polls put Merkel in a very strong position to win a fourth term, despite a loss of support notably over her welcome for a million asylum seekers last year. The SPD trails badly but could end up in a new grand coalition under Merkel.
Apart from Schulz, the other leading figure to be the SPD's choice for chancellor is party leader and vice chancellor Sigmar Gabriel, although other contenders could seek the mantle.
Schulz ran a bookshop in his native Aachen in western Germany before entering the European Parliament in 1994. As speaker of the body since 2012, he used new powers granted by the 2009 Lisbon Treaty to increase the legislature's role in EU politics and has used the post to raise his profile at home.