William Rogers, 90, a District of Columbia lawyer and Latin America expert who became a top adviser to Henry Kissinger at the State Department in the mid-1970s and afterward as an international consultant, died September 22 near Upperville, Va., after a heart attack during a fox hunt.

Rogers periodically interrupted his long career as a partner in the Arnold & Porter law firm for government assignments in Republican and Democratic administrations.

His most-remembered work as a public servant was in the mid-1970s, when he held two posts under Mr. Kissinger, who was secretary of state: assistant secretary for inter-American affairs and undersecretary for economic affairs. During those years, he played prominent roles in sensitive negotiations. They included planning the American handover of the Panama Canal, applying financial and political pressure to help end Ian Smith’s white regime in majority-black Rhodesia (now Zimbabwe) and holding secret talks with Cuban emissaries about softening relations with Fidel Castro’s regime. The last effort was scuttled when Castro sent troops to Angola during its civil war.

Rogers also served as a presidential envoy to investigate the 1980 slaying of Catholic American churchwomen in El Salvador by the country’s security forces. He also was appointed senior counselor to a Kissinger-led commission that made recommendations about military and economic assistance in Central America in the early 1980s.

In 1982, Rogers was among the founding employees of Mr. Kissinger’s New York-based international consulting firm and later became its vice chairman.

Rogers remained a staunch supporter of the former secretary of state, particularly after books and news accounts showed Mr. Kissinger’s public service in an unsavory light. Rogers was incensed about negative portrayals of Mr. Kissinger’s legacy on human rights — and, by extension, his own — especially regarding the American relationship with Chile during Augusto Pinochet’s dictatorship.

In 2003, he persuaded the State Department to distance itself from a statement by then-Secretary Colin L. Powell that the American policy toward Chile in the 1970s was “not a part of American history that we are proud of.” Rogers said of Mr. Powell: “He was implying that the U.S. was morally responsible for what happened in Chile. He bought the myth.”

Subsequently declassified American documents showed that Rogers pressed his boss to make human rights a central part of private discussions with Pinochet during Mr. Kissinger’s visit to Chile.

Mr. Kissinger praised Rogers this week, calling him a “great advocate of human rights” and an “absolutely dedicated man who stood for fundamental values.”

But Rogers’s influence on Mr. Kissinger is a matter of dispute. An authority on Chile, Peter Kornbluh, noted in his book “The Pinochet File” that a secret memorandum on Mr. Kissinger’s talks with Pinochet “reveals no effort at ‘moral persuasion,’ no mention of democracy and only minimal concern expressed on human rights.” William Dill Rogers — no relation to President Nixon’s Secretary of State William Rogers — was born May 12, 1927, in Wilmington, Del. He majored in international affairs at Princeton University and graduated from Yale University’s law school in 1951.