BRUSSELS — The Trump administration downgraded the diplomatic status of the European Union’s delegation to the United States last year without making a formal announcement or informing the bloc about the change, a European official said on Tuesday.

After protest from Brussels and discussion between the European Union and the Trump administration, the reclassification of the delegation and the consequent demotion of the ambassador, David O’Sullivan, is understood to have been reversed, at least temporarily, the official said.

Mr. Trump has been critical of multilateral institutions, and his secretary of state, Mike Pompeo, delivered a provocative speech in Brussels on Dec. 4 in which he questioned the value of multinational organizations and institutions like the United Nations and the European Union. Mr. Pompeo then asked whether the European Union was “ensuring that the interests of countries and their citizens are placed before those of bureaucrats here in Brussels.”

The next day, the European Union’s demotion from a member state to an international organization became clear at the funeral of President George Bush, when Mr. O’Sullivan’s name was not called in the expected order, dictated by diplomatic protocols. The names of diplomats who had gathered in Washington to pay their respects were spoken, as is custom, from the longest-serving to the newest ambassador, a European Union official told the German news agency Deutsche Welle. “But he was called up as the last person.”