Samuel H. Day, Jr., a journalist and opponent of nuclear weaons who led a leftist magazine in a landmark First Amendment court battle over the publication of an article on the hydrogen bomb, died on Jan. 26 of a stroke. He was 74 and lived in Madison, Wis.

Mr. Day was managing editor of The Progressive, a magazine based in Madison, in 1979 when it printed "The H-Bomb Secret: How We Got It, Why We're Telling It." The federal government tried to halt the article's publication, bringing the magazine to court in a First Amendment case that ultimately resulted in a victory for free speech advocates and journalists.

The son of a United States diplomat, Mr. Day was born on Oct. 3, 1926, in Media, Pa., and spent his early childhood in Johannesburg. He graduated from Phillips Exeter Academy in 1945 and from Swarthmore College in 1949. That year, Mr. Day began his journalism career as a copy boy for The Washington Evening Star.

During the Korean War, he served in the Army in Germany as a writer for Stars and Stripes, the military newspaper. He joined The Associated Press in San Francisco on returning to the United States. In 1953, he moved to its Boise, Idaho, bureau. From 1956 to 1974, Mr. Day worked at several Idaho newspapers, including the weekly Intermountain Observer in Boise, which was considered a crusading, muckraking newspaper. He was a reporter and editor there for about a decade.

In 1957, he married Kathleen Hammond in Modesto, Calif. His wife survives him, as does his brother, Christopher of Boca Raton, Fla.; a sister, Mayflower Day Brandt of Berkeley, Calif.; three sons, Philip and Joshua, of Madison, and Samuel H. III of Chicago; and six granddaughters.

After the Observer folded in 1973, the Days moved to Chicago, where Mr. Day became managing editor of The Bulletin of the Atomic Scientists, a journal started by World War II scientists to inform policy makers about the dangers of nuclear weapons.

In 1978, Mr. Day moved to Madison to edit The Progressive, a monthly magazine that addresses issues of peace and social justice. Within a year, he began planning the publication of an article by a freelance writer named Howard Morland. The article, which resulted in the court battle, contained details and sketches showing how a nuclear bomb worked.

The Energy and Justice Departments, backed by President Jimmy Carter, asked the magazine not to publish the article. When Mr. Day refused, the government asked a federal judge to grant a restraining order prohibiting publication. Federal officials argued that the material in the article was classified and that its publication would jeopardize national security. The order was granted.

Mr. Day and the other editors of The Progressive fought the decision, saying the information in the article came from public sources. The United States Court of Appeals eventually lifted the injunction, and the article was published in November 1979.

The next year, Mr. Day left the magazine to join an anti-nuclear-weapons organization sponsored by the American Friends Service Committee. In the last two decades, he participated in dozens of nonviolent protest activities, especially those against nuclear proliferation and military arms build-up. He was often arrested for demonstrations like entering missile silo enclosures and standing on silo lids. After being arrested with 13 others in 1988 for the simultaneous occupation of 10 missile silos in Missouri, Mr. Day served six months in federal prison.

In 1991, he was again imprisoned for entering a military installation and distributing anti-war-crimes pamphlets a day after the Persian Gulf war started. He had a stroke in prison that left him legally blind.

But Mr. Day continued to travel in the United States and abroad to advocate international peace. Last year, he wrote in an article published in newspapaers across the country on Memorial Day weekend that "if it is right to honor those who served in the cause of war, then it is equally right to honor those who served in the cause of resistance to war."