BERLIN (Reuters) - Almost half of Germany’s first-time voters back Chancellor Angela Merkel, a poll by the Forsa Institut showed on Tuesday, providing a strong backbone of support as she prepares to bid for a fourth term in September.

FILE PHOTO: German Chancellor Angela Merkel delivers her speech at 10th National Maritime conference in Hamburg, Germany, April 4, 2017. REUTERS/Fabian Bimmer

Among all potential voters, conservative Merkel had 43 percent support, compared to 32 percent for Martin Schulz, the chancellor candidate for the centre-left Social Democrats (SPD). But that lead extended to 47 percent against 29 percent among those aged 18 to 21, the poll showed.

“Young people know Chancellor Merkel, with whom they grew up,” said Manfred Guellner, who heads the Forsa institute. He said the poll showed that “especially young people are looking for stability and continuity in these uncertain times.”

The elder stateswoman of western European politics, Merkel has come under fire at home for initially opening Germany’s doors to more than one million refugees. Ahead of what is likely to be a close-fought ballot, she has toughened her stance on immigration in recent months.

She faced criticism on Tuesday from the SPD, the junior partner in her coalition government, after giving her chief of staff, Peter Altmaier, a leading role in drafting the election programme for her Christian Democrats (CDU).

The appointment of Altmaier, who coordinates policy on migrant issues within the coalition, “violates the established political rules,” SPD general secretary Katarina Barley told the RND newspaper chain.

Altmaier said on Twitter that, while he looked forward to helping shape the CDU’s programme, the party’s general secretary Peter Tauber would remain its election campaign manager, adding that the SPD had similar arrangements.

Measured by party, the Forsa poll - conducted for Stern magazine and broadcaster RTL - put Merkel’s CDU and their Bavarian sister party (CSU) at 36 percent, 6 percentage points ahead of the SPD of former European Parliament president Schulz.

A second survey by INSA for the mass-circulation Bild newspaper ahead of the Sept. 24 national election gave the CDU/CSU a 1.5 point lead

In the Forsa poll, the anti-immigrant Alternative for Germany (AfD) party, which had seen its support weaken in recent months, was steady at 8 percent. The AfD added 1 point to 10 percent in the INSA poll.

Both Merkel and Schulz are hoping to form new governments with smaller partners, but the two polls suggested another “grand coalition” of their parties is likely.