Thruston B. Morton, 74, a Kentuckian who was a former assistant secretary of State, congressman, and chairman of the Republican National Committee and served in the Senate from 1957 to 1969, died yesterday in his home in Louisville. He had cancer.

He was a member of the House of Representatives from 1947 to 1953, then spent three years as assistant secretary of State for congressional affairs during the Eisenhower administration. He won the first of two Senate elections in 1956. He retired from the Senate in 1969. He was GOP national chairman from 1959 to 1961.

During his years in Washington, Sen. Morton became a leader of his party's moderate wing. He became better known for his concern about international affairs than as an advocate of the interests of his state. He represented a rural, border state, yet called on the Republican Party not to ally itself with the forces of racial segregation in the South. He attacked leaders in both parties during the urban riots of the late 1960s, saying much of the debate on the riots was "irresponsible."

Urbane, wealthy, and Yale-educated, Sen. Morton could play the patrician or could become a blunt-talking, blunt-acting politician. He gained widespread respect for his parliamentary skills, his party leadership, and his political courage. In 1967, when most persons of his party and state probably supported the war in Southeast Asia, Sen. Morton came out against the Johnson administration's policies. A year later, Sen. Morton called for a halt to our policy of "high-handed interventionism."

Yet his power within his party in the Senate was formidable. He led a rebellion against the then-Senate Republican leader, Everett M. Dirksen of Illinois, urging approval of a U.S.-Soviet consular treaty that Dirksen sought to defeat. Dirksen eventually reversed his stand. He joined Sen. Morton, and a majority of the Senate Republicans in voting for the treaty. The treaty received the two-thirds majority it needed and passed.

By the end of his second term, Sen. Morton was being touted as either the next Republican Senate leader or its 1968 vice-presidential nominee. And although he had faced stiff Senate races in 1956 and again in 1962, he was expected by leaders of both parties to be unbeatable in his 1968 reelection race. It thus came as shock when Sen. Morton announced in February 1968 that he would not seek reelection and was leaving public life.

In a press conference in Louisville on Feb. 23, 1968 officially announcing his retirement, he said he was quitting "for very compelling personal reasons. To use an old Kentucky expression, I suppose I am just plain track sore."

The next day, an editorial in The Post deplored his decision. It said that "At 60, he is alert, vigorous and apparently in tune with the problems of the day. His decision to retire will entail severe losses to the Senate, the country, and the Republican Party. Congress has great need of well-informed men of moderate views who are still capable of vigorous activity."

During his last year in office, Sen. Morton served as cochairman of Nelson A. Rockefeller's unsuccessful bid for the 1968 Republican presidential nomination. He campaigned for Richard M. Nixon, the party's nominee, during the 1968 general election. Since leaving office, Sen. Morton had been a Louisville banker and president of the American Horse Council, an association formed to promote the horse industry.

Sen. Morton was a native of Louisville and a 1929 graduate of Yale University. He served with the Navy aboard mine-sweepers and destroyers in the Pacific during World War II. He then became president of the family grain and milling firm. It was sold to Pillsbury in 1951.

He was elected to Congress in 1946, and twice won reelection. He declined to run for reelection in 1952. During his years in the House, he voted for Greek-Turkish aid and the anti-poll tax bill, and opposed cuts in foreign aid. He also opposed the shrill anti-communist cliches that pervaded much of the political dialogue of the time.

He once said, "I think we have a rather myopic view of communism that doesn't help the cause of world peace. I hate communism. I deplore its atheistic qualities and all about it. But I think that if the Russians and ourselves could sit down together like grown men and say we're going to stop wars, why we could do it."

In 1956, he challenged Earle C. Clements for the Senate. Clements was a former governor, the incumbent senator, and was acting Democratic Senate leader at the time of the race. Sen. Morton beat him by a thin margin of 506,903 votes to 499,922.

Sen. Morton was the brother of Rogers C.B. Morton, a former Maryland congressman, secretary of the Interior under President Richard Nixon, and Republican National Chairman, who died in 1979.

Sen. Morton's survivors include his wife, Belle Clay Lyons Morton, two sons, Clay Lyons Morton and T. Ballard Morton Jr., and a sister, Jane Morton Norton, all of Louisville, and five grandchildren.