"It is better for all concerned, in particular for Greece, if the country leaves the euro temporarily," Hans-Werner Sinn, president of the influential Ifo Institute at Ludwig Maximilian University in Munich, wrote in an essay published two weeks ago.

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Asked about his position by e-mail, Mr. Issing answered indirectly, saying that countries that break the rules of monetary union -- as Greece did -- should have to fend for themselves.

"If a country does not comply with the conditions agreed on, it should not get further financial aid," he said. "A country which does not get further support has to decide what to do."

Mr. Issing and Mr. Sinn are both extremely influential, and their thinking provides an intellectual foundation for opinions widely held by ordinary Germans. Chancellor Angela Merkel is facing intense pressure within her own center-right party, some of whose members are pushing for a special party congress to discuss the debt crisis.