Emmet John Hughes, 61, a journalist and author, an adviser and speechwriter to President Dwight D. Eisenhower and Gov. Nelson A. Rockefeller of New York, and a teacher and researcher at the Eagleton Institute of Politics at Rutgers University, died of a heart ailment Sunday at his home in Kingston, N.J.

Mr. Hughes, who was born in Newark, N.J., graduated from Princeton University in 1941 with highest honors and a Phi Beta Kappa Key. He went on to Columbia, where he was a student of Prof. Carlton J. H. Hayes. In 1942, when Hayes was appointed U.S. ambassador to Spain, he took the young Mr. Hughes with him as press attache.

This was the first step in a career that was to take Mr. Hughes to the upper reaches of government, journalism, politics and academia. He recorded his impressions and experiences in a number of books. Among the most notable were "America the Vincible," which appeared in 1959 and detailed Mr. Hughes' perceptions of the weaknesses of American foreign policy; "The Ordeal of Power," a memoir of the Eisenhower presidency which appeared in 1963, and "The Living Presidency," which was published in 1973.

Mr. Hughes spent World War II in Madrid. While he was press attache at the embassy, he enlisted in the Army as a private -- special permission for this was asked and received -- and served in the Office of Strategic Services, the wartime predecessor of the Central Intelligence Agency. In 1947, he published "Report from Spain," a book that was highly critical of the Franco government.

His work in Madrid brought him to the attention of Henry Luce, the founder of the Time, Inc. Luce sent him to Rome as the Time-Life bureau chief. He spent 1948 and 1949 as bureau chief in Berlin. This was the period of the Berlin Blockade, which was established by the Russians, and the Berlin Airlift, the successful American effort to offset it.

In 1952, Luce loaned his protege to the Eisenhower campaign staff as a speechwriter. He helped write the general's famous "I shall go to Korea" speech in which he promised to try to end the Korean war. He drafted Eisenhower's first inaugural address and other major statements. He served briefly in the White House in 1953 and then returned to Time-Life. In 1956, he worked for Eisenhower's reelection.

Mr. Hughes and the president remained personal friends until the publication of "America the Vincible." Their relationship could not withstand Mr. Hughes' criticisms of the president's foreign policy. John F. Kennedy, then a senator, described it as "a passionate, quite remarkable book."

In 1960, Mr. Hughes resigned from the Luce organiztion to become a special assistant to Gov. Rockefeller. In 1963, he joined Newsweek, a publication of The Washington Post Co., as a columnist. From 1968 to 1970, he served again on Rockefeller's staff. He then went to the Eagleton Institute at Rutgers.

Among Mr. Hughes' abiding interests were the Catholic Church and presidential power. Catholicism provided the subject of his first book, "The Church and The Liberal Society." An expansion of his senior thesis at Princeton, when he was still planning a career as a scholar, it was an examination of the church in a democratic society. It appeared in 1943.

At Rutgers, Mr. Hughes was able to resume his earlier intentions to teach and write. The result was "The Living Presidency." The historian Henry Steele Commager described it as "quite simply the most thoughtful and the most perspicacious book on the Presidency that I have ever read."

Mr. Hughes' marriages to Marifrances Hughes, the former Eileen Lanouette and the former Katherine Nouri ended in divorce.

Survivors include a son by his first marriage, John, of Los Angeles; two daughters by his second marriage, Mary Larkin Hughes and Kathleen Hughes, both of New York City, and two daughters by his third marriage, Caitlin and Johanna Hughes of Princeton, N.J.