John A. Baker, 68, the assistant secretary of Agriculture for rural development and conservation from 1962 until 1969 and a former legislative director of the National Farmers Union, died of congestive heart failure March 2 at Arlington Hospital. He lived in Arlington.

Mr. Baker was a native of Paris, Ark., graduated from the University of Arkansas and earned a master's degree at the University of Wisconsin.

He moved to Washington in 1937 when he joined the Department of Agriculture as an economist. He was transferred to Arkansas in 1939 as a regional administrator with the Farm Security Administration.

During World War II, Mr. Baker served with the Navy in the Pacific. After the war, he remained in South Korea with the U.S. military government as a director of the National Land Administration.

He returned to Washington in 1949 as executive assistant to the under secretary of Agriculture.

Mr. Baker joined the National Farmers Union in 1951. He resigned in 1961 and returned to the Agriculture Department as director of agricultural credit. President Kennedy appointed him assistant secretary in 1962.

In 1964, he created the "adjusted parity ratio," which appears in the monthly USDA Agricultural Prices report to indicate the value of farm commodity program payments as an elemnt in farm income.

From 1974 until he retired in 1979, Mr. Baker was executive vice president of the National Farmers Union Green Thumb Program, a federally funded program providng community employment for the elderly.

Survivors include his wife, Susan T. Baker of Arlington; five sons, Roger, of League City, Tex., James, of West Newton, Mass., Robert, of Arlington, David, of Milwaukee, and Gordon, of Richmond; a daughter, Judith, of Richmond, and seven grandchildren.