BERLIN — The election bid of Germany’s foreign minister, Frank-Walter Steinmeier, against Chancellor Merkel next year will pit the coalition government’s top two officials against each other.

A Social Democratic Party shake-up backed by senior members in Berlin yesterday leaves Mr. Steinmeier, the chief of staff for Chancellor Schroeder, as its candidate for the September 2009 election. That threatens 12 months of political impasse between the Social Democrats and their coalition partners, Ms. Merkel’s Christian Democrats, just as the economy stumbles.

“The coalition, already under strain, will become dysfunctional,” the managing director of polling company Psephos, Hans-Juergen Hoffmann, said in an interview. “The coalition parties will be preoccupied with defining, honing their differences, rather than working on a common policy as the economy cools. The election has clearly begun.”

Mr. Steinmeier, 52, who has never held an elected position, was unanimously nominated as chancellor candidate by party leaders. Franz Muentefering, 68, was proposed as party chairman in place of Kurt Beck, 59, who unexpectedly quit the post yesterday citing “false information” spread by the press giving him “no room to maneuver and make decisions.” A special party meeting will be held October 18 to vote on both nominations.

“I know what’s expected of me,” Mr. Steinmeier told reporters in Berlin yesterday. “I have respect for the office; I’ve known the chancellery from the inside for many years. I’m not entering the race for the sake of taking part, but to win.”

The Social Democrats, known as the SPD in German, and the Christian Democrats formed a coalition in November 2005 after elections left them unable to form a government on their own or with their preferred partners.

Mr. Beck, who became SPD chairman in April 2006, leaves the party trailing the Christian Democrats by as many as 16 percentage points in polls and with membership on the slide as the anti-capitalist Left Party makes gains among the SPD’s traditional supporters. The Left, which comprises former East German communists and disaffected ex-SPD members, is shunned by all parties at a national level.

“Beck is gone but the SPD’s problems remain unresolved,” the general secretary of the Christian Democrat, Ronald Pofalla, told reporters yesterday. “We need a stable coalition partner. Germany can’t grind to a standstill.”

Ms. Merkel congratulated Mr. Steinmeier, though she said the manner of his appointment showed the “deep discord” within the Social Democratic Party, Deutsche Presse-Agentur reported, citing comments made by the chancellor in Munich.

The foreign minister, who also holds the post of vice-chancellor, represents the SPD’s best chance of closing the Christian Democrats poll lead, according to a politics professor at Berlin’s Free University, Paul Nolte.

In foreign policy, Mr. Steinmeier has sought to avoid isolating Russia after its war with Georgia and opposed Ms. Merkel’s decision in 2007 to meet the Dalai Lama, concerned it would strain ties with China. Ms. Merkel wants to drop plans to scrap nuclear energy and opposes Social Democrat hopes of introducing a minimum wage.