Simon Kuznets, 84, a Harvard professor whose work in developing the concept of the gross national product earned him the Nobel Prize in economics in 1971, died July 9 at his home in Cambridge, Mass., after a heart attack.

The citation accompanying his Nobel award spoke of his "empirically founded interpretation of economic growth which has led to new and deepened insight into the economic and social structure" and his work in "illuminating with facts -- and explaining through analysis -- the economic growth from the middle of the last century."

Dr. Kuznets' work in incomes accounting not only illustrated problems of national economic growth, but also transformed economics from an ideology into a science. He applied statistical methods to measuring sources of a nation's wealth. He analyzed population changes, marketing patterns, the growth of technology and the structure of industry to determine change in economic growth.

His fame came not from founding philosophical schools of economic thought or new and catchy theories concerning the "dismal science," as William Ewart Gladstone called it, but rather for his brilliant organization and interpretation of data.

Fellow economist and Nobel laureate Paul Samuelson said, "Simon Kuznets was the founder of national income measurement, and he created quantitative economic history."

John Kenneth Galbraith, another member of the Harvard economics faculty, a widely read author and a former government official, said: "When we speak of gross national product, national income, their components and the policies pertaining thereto, it is the structure created by Kuznets that we address."

Galbraith called the gross national product (GNP), which is the value of all the goods and services produced by an economy in a given period, "one of the greatest discoveries of all time."

Dr. Kuznets earned his bachelor's, master's and doctoral degrees at Columbia University. In addition to teaching at Harvard, he was a member of the faculties at the University of Pennsylvania and Johns Hopkins University. But his most important work was with the National Bureau of Economic Research, a private, nonprofit agency with which he was affiliated from 1927 to 1960.

His work on the GNP resulted from a project that the NBER did for the Senate in the 1930s. The federal government had no real measurement of the nation's economic health. Dr. Kuznets and the bureau provided it.

In 1941, Dr. Kuznets published his two-volume work, "National Income and its Composition, 1919-38." Other works by Dr. Kuznets included "Economic Growth of Nations." During World War II, Dr. Kuznets was associate director of the Bureau of Planning and Statistics at the War Production Board.

He was a past president of both the American Economic Association and the American Statistical Association and a fellow of the Econometric Society.

Dr. Kuznets was born in Kharkov, the Ukraine, and came to this country in 1922. He joined the faculty at the University of Pennsylvania in 1930, taught at Johns Hopkins from 1954 to 1960, and then moved to Harvard, where he was made professor emeritus in 1971.

Survivors include his wife of 56 years, the former Edith Handler, of Cambridge; a son, Paul, of Bloomington, Ind.; a daughter, Judith Stein of Rochester, N.Y.; a brother, George, of Berkeley, Calif., and four grandchildren.