By Andrea Shalal and Michelle Martin
BERLIN (Reuters) - Chancellor Angela Merkel's chief of staff will become acting finance minister when Wolfgang Schaeuble leaves office, Sueddeutsche Zeitung said on Friday in a report that the government's spokeswoman did not deny.
Without identifying its sources, the newspaper said Merkel had decided Peter Altmaier would take over from Schaeuble, who agreed on Wednesday to become parliament president to clear the way for someone from another party to take his job.
Government spokeswoman Ulrike Demmer told reporters she would not deny the news report, but said the lower house of parliament would not elect a new president until its first session, which must take place by Oct. 24.
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"We will inform you about everything promptly after that," Demmer told a regular news conference.
Altmaier, a conservative and close confidant of Merkel's, would take over after the 75-year-old Schaeuble is nominated by the conservative alliance at a meeting on Oct. 17, the report said.
He would then hand over to whoever is named by a new coalition partner, probably the pro-business Free Democrats (FDP).
Fifty-nine percent of Germans support Merkel's aim to create a three-way coalition with the FDP and the environmentalist Greens, a survey for broadcaster ZDF found.
But a so-called "Jamaica" coalition - after the parties' colors of black, yellow and green that match the Jamaican flag - has never been tested at the national level and there are serious differences on migration, energy, taxes and Europe.
Complicating coalition talks is a debate between Merkel's Christian Democrats (CDU) and their Bavarian sister party, the CSU, which lost 10 percentage points in Sunday's vote.
Eager to claw back support ahead of state elections in 2018, the CSU has redoubled its calls for limiting migration, something Merkel has opposed.
Only 23 percent of Germans would favor the continuation of a "grand coalition" of Merkel's conservatives and the SPD, which governed for the last four years.
Almost two-thirds of those polled supported the SPD's decision to go into opposition at the national level after its worst election result in the post-war era on Sunday.
Andrea Nahles, the SPD's newly elected parliamentary leader, said the conservatives, the FDP and Greens "need to and will get it (a coalition agreement) done".
"If Chancellor Merkel thinks the SPD is a tactical reserve option for an emergency, then she is wrong," Nahles told Bild.
Merkel's chief of staff suggested negotiations may take longer than four years ago, when a deal was reached by Christmas.
"That's what I'm hoping for, but what's decisive is the substance, not the date," Altmaier said in an interview published by Focus magazine on Friday.
Exploratory talks are due to begin after an Oct. 15 election in the state of Lower Saxony, now ruled by a coalition of the SPD and Greens.
(Reporting by Michelle Martin and Andrea Shalal; Editing by Robin Pomeroy)