Noted Civil War historian and lecturer E.B. (Pete) Long, 61, died Tuesday in Chicago of an apparent heart attack.

Mr. Long, a professor of American studies at the University of Wyoming, died at a downtown hotel. He was in Chicago to address the Chicago Press Club and the Civil War Round Table with his latest book, "The Saints and the Union: the Utah Territory during the Civil War," a study of the Mormons during that conflict.

He was perhaps best known for his detailed, definitive record of the North-South conflict called "The Civil War Day by Day," on which he was helped by his wife, Barbara. It was a distillation of the 9 million words on 26,000 pages that he had compiled on that war after visiting 125 universities and libraries throughout this country.

Mr. Long was born in Whitehall, Wis., and attended Miami University in Oxford, Ohio, and Northwestern University. He did not finish all the requirements for a degree, because of his dislike for the foreign language he was studying. Nevertheless, from 1967 to 1969, he served as visiting lecturer in history at the University of California in Riverside and at San Diego, and at the University of Illinois in Chicago.

Before that, beginning in 1955, Mr. Long had served as director of research for the renowned historian Bruce ycatton's project, the centennial history of the Civil War. He also worked for historian Allan Nevins on the eight-volume work, "Ordeal of the Union."

Mr. Long had earlier worked for the Associated Press in Chicago and the Chicago Tribune.

He is survived by his wife, Barbara, of Laramie, Wyo.