BERLIN, DEC. 17 -- Lothar de Maiziere, East Germany's first and last freely elected prime minister, today resigned his cabinet and party positions in the German government after failing to disprove charges that he was an informer for the Communist regime's Stasi secret police.

Despite his surprise exit, de Maiziere, 50, continued to maintain that he did not deliver information about dissidents and church activists to the reviled Stasi.

But in an interview with The Washingon Post tonight, the chief of the German government agency that has custody of more than 6 million Stasi files said that although the main file on de Maiziere is missing, there is no reason to doubt the authenticity of other documents that indicate he gave information to the Stasi.

"It could be that he cooperated in some way with a good motivation, perhaps to maintain good relations between the state and the church," said the Rev. Joachim Gauck, the Protestant minister in charge of the Stasi files. "He says he has a clear conscience, and that can be true.

"But even if he only cooperated a little, why should he be at the top of our new society? People should first look into their past and then decide whether to go into politics -- not the other way around. Perhaps de Maiziere is a victim, but he should have told people, 'Look, this is what happened.' He should start remembering."

After meeting with Chancellor Helmut Kohl to discuss the spying charges, de Maiziere said he will retain his parliamentary seat while giving up his jobs as deputy chairman of Kohl's Christian Democratic party and minister without portfolio in Kohl's cabinet.

Kohl, who was considering making de Maiziere justice minister in his new government, responded to the resignation with regret. "I respect Lothar de Maiziere's decision," Kohl said. "It has moved me deeply. Lothar de Maiziere has won my full trust, and even today I have no reason to doubt his word."

The accusation against de Maiziere emerged last week, after investigators found a card on which an informer code-named "Czerny" is listed with de Maiziere's home address. Former Stasi agents told German newsmagazines that de Maiziere had worked for the secret police for eight years, voluntarily filing reports on the Evangelical Church, the base of East Germany's small dissident movement.

De Maiziere was a lawyer before he entered politics and represented the church and dissidents. He was not a Communist and was active in the East German Christian Democratic Union, a small party that never challenged the Communist regime.

Interior Minister Wolfgang Schaeuble, who investigated de Maiziere's case for Kohl, said today that the Stasi records indicate, but do not prove, that de Maiziere, a former professional viola player, was Czerny. Carl Czerny was a 19th-century Austrian composer.

Although he initially maintained that he had nothing to do with the Stasi, de Maiziere last week conceded that his legal work brought him into contact with the secret police but said he had never written reports or done anyone harm.

"Since last autumn, I have given all I had to help build free, democratic and just conditions in a united Germany," de Maiziere said, asking the government to continue its probe of his case. "I won friends and obviously made enemies too."

Gauck said there is no reason to believe the documents in de Maiziere's case were falsified or tampered with. "The files are in much better condition than has been thought," he said.

In his six months as the only elected prime minister in East Germany's 41-year history, de Maiziere fought against West German efforts to eliminate all traces of the Communist state, managing to save some industrial jobs and win a role for eastern politicians in the new all-German government.

But with de Maiziere following in the path of several other eastern leaders who have had to resign because of Stasi connections, only one east German remains under consideration for a cabinet post in the reunited country's first government.

De Maiziere was virtually unknown even after he was elected prime minister in March. The east's Christian Democrats had based their campaign on the prospect of unification and Kohl's promise of a better, Western lifestyle. De Maiziere became the party's top candidate only four days before the vote, after candidate Wolfgang Schnur admitted his Stasi contacts and quit the race.

In an interview with The Post shortly before the two Germanys reunited in October, de Maiziere said that "a difficult situation has arisen, in which the accused must now prove their innocence. I'm opposed to all forms of collective guilt. Guilt is always of the individual.

"I believe that those who lived in this situation for 40 years have more right to judge than those who did not live under such conditions. I do not wish to say anything more on this issue."