PARIS — Nearly 150 leading economists on Tuesday criticized President François Hollande’s plan to appoint a former executive of France’s largest lender to head the country’s central bank by calling on legislators to block the appointment over concerns about potential conflicts of interest.

Mr. Hollande said last week that the executive, François Villeroy de Galhau, formerly co-chief operating officer at BNP Paribas, would head the Banque de France, succeeding Christian Noyer, who is to step down at the end of October. The choice of Mr. Villeroy de Galhau came as something of a surprise, as Benoît Coeuré, a French member of the European Central Bank’s Executive Board, had been expected to win the job.

Though the European Central Bank is responsible for monetary policy in the eurozone, the Banque de France has an essential role in helping to execute that policy and in regulating the country’s banks. In addition, the heads of the central banks of the eurozone’s 19 member states are members of the E.C.B.’s Governing Council, the organization’s main policy-making body.

The Élysée Palace did not respond to requests for comment. The Banque de France declined to comment.

Mr. Villeroy de Galhau did not respond to requests for comment. But in a Sept. 8 letter to Mr. Hollande that was obtained by The New York Times, Mr. Villeroy de Galhau noted that he had spent 20 years in public service before joining BNP Paribas, and said he would go beyond the letter of the law to ensure he was on a sound ethical footing.

Mr. Villeroy de Galhau said in the letter that he was not due any remuneration from BNP Paribas, and that he would hold no shares in the bank once he had disposed of stock that he could not legally sell until next year. He also played down the prospect that his regulatory mandate would allow for any possible partiality toward his former employer.

He also pledged to recuse himself “from any individual decision involving BNP Paribas or its subsidiaries” for two years.

Choosing a new central bank chief is often a difficult task for a political leader, and there is plenty of precedent for appointing former bankers to the job. For example, Mario Draghi, the European Central Bank president, is a former vice chairman and managing director of Goldman Sachs.

Though Mr. Villeroy de Galhau served for years in French government posts before he joined BNP Paribas in 2003, his selection raised eyebrows among some who thought the revolving door was perhaps swinging a bit too swiftly for comfort: Having left BNP Paribas in May, he would be expected to enforce the eurozone’s banking regulations on his former colleagues just months later, they argued.

The rumblings of discontent broke out into the open on Tuesday. The French academic economists, writing in Le Monde, observed that Mr. Villeroy de Galhau’s experience “without a doubt confers upon him an excellent expertise in the banking sector, at least as much as it exposes him to grave conflicts of interest and undermines his independence.”

“It is utterly unrealistic to think that one can have served the banking industry, and then, a few months later, regulate it with impartiality and complete independence,” the letter adds.

The signatories included some of France’s best-known economists, including Thomas Piketty, a professor at the Paris School of Economics and author of a best-selling book, “Capital in the Twenty-First Century.”

The economists’ letter was addressed to leaders of the two houses of the French Parliament, where finance committees must still approve Mr. Villeroy de Galhau’s appointment.

The technocratic Mr. Villeroy de Galhau had a gilded career as a civil servant, like Mr. Noyer and, indeed, most of France’s recent central bank governors. A product of the elite École Polytechnique and a fluent German speaker, he served as a government auditor and later as chief of staff to two former finance ministers, Dominique Strauss-Kahn and Christian Sautter. He also served as head of the French tax administration from 2000 to 2003.

“Are our political leaders now such prisoners of financial interests that they leave it to finance the power to name their own to key roles in the bodies that are supposed to regulate them?” the letter asked. “Are they so out of touch that they don’t appreciate the deleterious effect such a decision has on our democracy?”

Without identifying Mr. Coeuré by name, the economists’ letter suggests that his résumé, which includes his being a French economist, a former Treasury director and a current member of the E.C.B.’s Executive Board, showed that he would have been a more suitable candidate having the necessary expertise as well as the necessary independence from political pressure and the banking lobby.

Nicolas Véron, a French economist with the Peterson Institute for International Economics, said that the public outcry had resulted from “a perception that the process was biased,” and that Mr. Villeroy de Galhau had been chosen as much “for political considerations and personal considerations” as for his qualifications. As a representative of the highest levels of the country’s technocratic elite, his victory shows the strength “of the French caste system,” Mr. Véron said.

Mr. Villeroy de Galhau “is an unknown quantity as a central banker,” said Mr. Véron, who did not sign the economists’ letter. “He’s very smart and well connected, but he’s untested on all the key points, except politics, whereas Mr. Coeuré is well known.”