FRANKFURT — The head of the Swiss central bank unexpectedly resigned Monday, saying that doubts about currency trades he and his wife made last year threatened to undermine his ability to focus on steering the bank through a global financial crisis.

The departure of the bank chief, Philipp M. Hildebrand, 48, cut short the public career of a major international advocate of stricter banking regulation. He quit as the Swiss National Bank fought to keep the country’s currency from becoming so strong that Swiss companies could not sell products abroad.

But analysts predicted the central bank would maintain a limit it set on the franc’s appreciation against the euro, by vowing to buy unlimited amounts of foreign currency. “It may be that some speculators will try to test the market, but we’re convinced that the S.N.B. will continue to defend the exchange rate,” said You-Na Park, an analyst at Commerzbank in Frankfurt.

Appearing before reporters in Bern, the Swiss capital, Mr. Hildebrand said he would also resign immediately from several international posts, including vice chairman of the Financial Stability Board. The panel of central bankers and regulators has played a discreet but influential role in establishing rules for big international banks that are likely to be adopted by most large countries.