BERLIN — After ignoring the issue of Afghanistan for much of the federal election campaign so far, the Free Democrats, an opposition party that hopes to join Chancellor Angela Merkel’s conservatives in the next government, have called for a plan to bring home the 4,500 German troops serving in the NATO force there.

In doing so, the party has broken ranks with most of the major parties, which have tried to keep the issue of Germany’s controversial Afghan presence out of the public eye.

“The next government must formulate a precise plan that spells out how a pull-out of the German Army over the coming years would look,” Jürgen Koppelin, a federal legislator and defense expert for the Free Democrats, said in a newspaper interview Wednesday. “Our soldiers in Afghanistan and their families need to know that the mission will end.”

By raising the issue now, the Free Democrats may be trying to show their foreign policy credentials, particularly since they hope to take over the Foreign Ministry if they win enough votes to form the next coalition with Mrs. Merkel, who is favored to retain the chancellery. So far, foreign policy issues have played no role in this campaign, which has yet to get going in force.

The Free Democrats have also tapped into the public mood, which may win them more votes.

According to opinion polls, the majority of those asked say they are opposed to German soldiers remaining in Afghanistan. That view reflects the anti-war attitude that has been ingrained in the populace since 1945.

Mrs. Merkel and her governing partner, the Social Democrats, have not engaged the Afghan issue in any substantive way during the campaign, hoping to avoid having it become the topic of an incendiary debate that could significantly affect the voting.

Only the opposition Left Party, a relatively new grouping of former East German communists and West German trade unionists, has been consistently outspoken about Afghanistan, demanding the immediate end of the mission. But it is viewed as a strident voice on the subject, and its calls have been ignored by the government and other opposition parties.

Internationally, Germany has been the target of much criticism from its NATO allies — particularly Britain, Canada, Denmark, the Netherlands and the United States — whose troops have borne the brunt of the fighting in southern Afghanistan.

German troops are based in the northern province of Kunduz, which had been relatively peaceful until the Taliban established a foothold there. The government in Berlin has refused to send any troops to join NATO and U.S. forces in the south on the grounds that their presence in the north is needed.

The Free Democrats’ stance on the issue just as the election campaign takes off caught Mrs. Merkel’s coalition of conservatives and Social Democrats off guard.

On Thursday, Franz Josef Jung, the conservative defense minister, who has refused to use the word “war” to describe the operations of the German contingent, told ARD, the public television channel, that it was possible the army could remain in Afghanistan for 10 more years, until that nation’s security forces have been trained.

Frank-Walter Steinmeier, the Social Democrat foreign minister who will run against Mrs. Merkel for the chancellery, echoed that sentiment.

He told the Leipziger Volkszeitung that he believed German soldiers could be in Afghanistan for 10 more years “or longer.” That will not go down well with his party, which has a strong pacifist wing that opposes the Afghan mission.

Critics of the government’s policy say it has never adequately explained to the public the strategy and goals of the mission.

Among those critics is the Federal Armed Forces Association, a politically independent institution that represents more than 210,000 soldiers.

“What is needed more than ever is public support for our men and women serving in Afghanistan,” said Wilfried Stolze, the association’s spokesman. “But the politicians, including the chancellor, have shown no courage in explaining to the public why our troops are there in the first place.”

Mrs. Merkel, who has made two visits to Afghanistan since becoming chancellor nearly four years ago — in late 2007 and last April — has never broached the subject during a prime-time television interview, a speech or a public rally, nor has she suggested that the foreign affairs or defense committees of the Bundestag, or Parliament, hold hearings on the issue.

Mr. Stolze said that his group had reservations about the Free Democrats’ call for a withdrawal plan, but that it approved of the question being put forward publicly so that it could be debated.