Hamilton Fish Sr., 102, the New York Republican whose 25 years in the House of Representatives brought him fame for the causes he led and the political enemies he made, died Jan. 18 at his home in Cold Spring, N.Y. He had kidney and heart ailments and pneumonia.

He gained national fame as a leading voice of isolationism before World War II. Mr. Fish, who served in Congress from 1920 to 1945, was the ranking Republican on both the House Rules and Foreign Affairs committees at the time, giving him immense power. And his constituents included President Franklin D. Roosevelt, which seemed to anger the president to no end.

Mr. Fish, who was an early proponent of hunting domestic communists, whom he felt were much more dangerous than any menace from Nazi Germany, became a national leader of the movement to keep this country out of World War II. He spoke at huge rallies and used his influence in Congress to become one of Roosevelt's more vocal and threatening, if not successful, foes.

He led House opposition to Roosevelt's calls for the draft and extension of the draft, and to Lend-Lease to aid Britain in the war. Though the president gained narrow victories in each of these battles, he came to attack three of his congressional foes by referring to them as "Martin, Barton and Fish."

In the pre-war days of the late 1930s, many emotional voices were raised for and against a rising Germany. Mr. Fish once spoke at a 1938 German Day rally at Madison Square Garden from a stage decorated with swastikas, and flew to a meeting of the Interparliamentary Union in Oslo in the summer of 1939 in a plane belonging to the German foreign minister.

However, once the United States went to war in 1941, Mr. Fish called upon the nation to unite behind the president. He also remarked that what he most wanted to do was return to the battlefield in uniform.

Roosevelt was not his only political foe. Both Wendell Willkie and Thomas Dewey, the Republican presidential nominees in 1940 and 1944, worked for his defeat. Dewey, as governor of New York, was in position to do something about it. He helped engineer a redistricting that contributed to Mr. Fish's defeat in 1944. However, in the 1970s, Mr. Fish returned to news headlines as a vocal defender of President Nixon.

Mr. Fish, scion of a family long associated with public service, was a former Harvard University football lineman, team captain and all-America tackle, and an Army combat veteran of World War I. Though he started out in the New York Assembly as a Democrat and a progressive, he had become a conservative Republican by the time he arrived in Congress. He has been described as big-boned, yet rather handsome, and was known for a speaking style that featured a booming voice and windmilling arms.

His great-grandfather, Col. Nicholas Fish, served on the staff of Gen. George Washington. His grandfather, Hamilton Fish, was a U.S. representative and senator from New York and governor before serving as secretary of state under President Ulysses S. Grant from 1869 to 1877. His father, also named Hamilton Fish, served in Congress from 1909 to 1911. His son, Hamilton Fish Jr., has held his father's old congressional seat since 1969.

Hamilton Fish Sr. was born in Garrison, N.Y. After graduating cum laude from Harvard in 1910, he attended its law school for a year, then served in the state Assembly from 1914 to 1916. He went to war as a captain and led black troops in battle, receiving the Silver Star. He later became a colonel in the Army Reserve.

He won a special election to the House of Representatives and took his seat in November 1920. He represented New York's 26th District, which included the Hudson Valley counties of Orange, Putnam and Dutchess, and Hyde Park, the Roosevelt home.

In addition to opposing communism and U.S. entry into World War II, he championed a number of causes. He introduced bills to provide for the Tomb of the Unknown Soldier; to make the Star-Spangled Banner the national anthem; and to call upon the football teams of the U.S. Military Academy at West Point and the U.S. Naval Academy at Annapolis to play an annual game. He also favored some civil rights and prison reform.

In 1930, he introduced legislation calling for the creation of a committee to investigate communist activities in this country.

The bill passed and he became the committee's chairman. The "Fish Committee," as it inevitably became known, was not successful in finding much subversion.

His first wife, the former Grace Chapin, whom he married in 1921, died in 1960.

In 1966, he married Marie Blackton. After her death, he married Alice Desmond in 1976. They divorced in the early 1980s.

Survivors include his wife, the former Lydia Ambrogio, of Cold Spring; and two children by his first marriage, Rep. Hamilton Fish Jr. and Elizabeth Pyne of New Jersey.