BERLIN: German President Horst Koehler hopes to secure a second five-year term on Saturday in an unusually tight contest that comes just months before the country chooses a new government.

Koehler, 66, is a member of Chancellor Angela Merkel's conservative Christian Democrats and a former head of the International Monetary Fund.

Polls show that he has become one of Germany's most popular politicians, but his re-election by a special parliamentary assembly is not assured.

Gesine Schwan, 66, a center-left Social Democrat and former university professor, is challenging Koehler in a rerun of the 2004 presidential vote. She hopes to become the first female head of state.

The presidency, which is largely ceremonial but carries moral authority, is supposed to be above the political fray.

However, this year's contest comes four months before Merkel and Social Democrat Frank-Walter Steinmeier, her foreign minister, face off in a national election in which both hope to end their tense "grand coalition" of Germany's biggest parties.

Merkel, then Germany's opposition leader, installed Koehler in 2004 with the help of the pro-business Free Democrats, her preferred future coalition partner.

A defeat for Koehler would be a symbolic blow to Merkel before September's vote and a surprise success for the Social Democrats, who have been lagging in polls.

The choice will be made by a special 1,224-member assembly split equally between lower-house lawmakers and delegates nominated by Germany's 16 state legislatures. Those delegates range from Germany's main Jewish leader, Charlotte Knobloch, to national handball team trainer Heiner Brand.

Merkel's party and the Free Democrats have 604 votes. Together with the Free Voters, a small Bavarian center-right party, they could muster 614, just enough to re-elect Koehler.

However, the ballot has been somewhat unpredictable in the past, with some delegates defying parties' wishes.

A candidate needs an absolute majority in the first two rounds of voting; if the ballot goes to a third round, a simple majority is sufficient.

Schwan would need support from the opposition Left Party to win, which could be awkward for the Social Democrats. They have ruled out forming Germany's next government with the party, which opposes German military deployments abroad and economic reform.

The Left Party has its own long-shot candidate, television actor Peter Sodann.

A far-right candidate, Frank Rennicke, is expected to make no significant impact.

Koehler has positioned himself as an outsider to Germany's political elite. He has occasionally refused to sign bills into law because of constitutional concerns, and recently warned politicians against using the financial crisis as a "backdrop for posturing."

Schwan says she wants to help bridge the divide between people and politicians.