Foreign Minister Hans-Dietrich Genscher, who helped guide Germany to unification and waged a long campaign for closer ties among European nations, stunned Germany today by announcing his resignation.

Chancellor Helmut Kohl named Irmgard Schwaetzer, the Housing Minister and a former aide to Mr. Genscher, to be the new Foreign Minister. Mrs. Schwaetzer, 50 years old, will be the first woman to hold a senior Cabinet post in Bonn.

Mr. Genscher's 18 years in office, serving with both Christian Democratic and Social Democratic Chancellors, make him the world's senior foreign minister. His resignation takes effect on May 7, but he will remain in Parliament and is likely to continue to be influential in the Free Democratic Party, Germany's third party and the junior partner in the ruling coalition with Mr. Kohl's conservative Christian Democratic Union.

The leader in Parliament of the Social Democrats, Hans-Ulrich Klose, called the resignation "the beginning of the end of the Kohl Government."

Mr. Kohl, at a news conference, sought to counter such notions. "I cannot see any weakening of the Government in this at all," he said.

The 65-year-old Mr. Genscher did not specify his reasons for quitting. However, he has suffered two heart attacks and associates said he is increasingly concerned about his health.

In addition, he has been a target of growing criticism from politicians and commentators who assert that he was losing his deft political touch, something that made him widely admired.

"I am fully convinced that this decision is correct and necessary," Mr. Genscher...