It marked one of the first times that Mr. Apol, who also serves as the agency’s general counsel, made a public statement questioning ethical standards in the Trump administration.
Mr. Apol also recently clarified federal rules regarding the creation of legal defense funds for officials that become subjects of investigations. Mr. Trump; Vice President Mike Pence; Donald F. McGahn II, the White House counsel; Jared Kushner, the president’s son-in-law and senior adviser; and Hope Hicks, the White House communications director, have hired lawyers related to the continuing investigation by Robert S. Mueller III, the special counsel conducting the Russia investigation.
Mr. Apol suggested that public confidence in the government could be undermined if federal employees — and ethics officers at each agency charged with overseeing them — do not take steps to strengthen their commitment to ethical governance.
“As a leader in the United States government, the choices that you make and the work that you do will have profound effects upon our nation and its citizens,” Mr. Apol wrote. “It is essential to the success of our republic that citizens can trust that your decisions and the decisions made by your agency are motivated by the public good and not by personal interests.”
Federal employees, he wrote, must be thinking more about “what conduct is, and is not, permissible.”
The Office of Government Ethics is a tiny agency that has seen its profile surge in recent months, as questions have surfaced about actions by Mr. Trump, such as his continued ownership of a real estate business while in the White House, and some of his top aides, including the recommendation by Kellyanne Conway, a senior Trump adviser, in a television interview for people to buy products sold by Ivanka Trump’s retail brand.
It oversees ethics compliance in 130 executive branch agencies, covering 2.7 million civilian employees.
Mr. Apol replaced Walter M. Shaub Jr., an appointee of President Barack Obama, who was frequently critical of Mr. Trump.