Joazuin Garrigues-Walker, 46, the leader of the radical wing of the governing Central Democratic Union Party and a man who helped shape Spain's politics after the death of Generalissimo Franciso Franco, died Monday of a heart attack. He had leukemia.

The son of a wealthy Spanish father and an American millionairess, Mr. Garrigues-Walker studied law at the University of Madrid. During this period, when Franco still was in power, he was twice arrested. In 1957, he went to the United States to work for the Chase Manhattan Bank.

In the early 1970s, the last years of Franco's rule, he formed a "society for free studies," which became the Democratic Party. After Franco's death in November 1975, Mr. Garrigues-Walker became president of his party. The group later merged with the Central Democratic Union.

Mr. Garrigues-walker joined the government as minster of public works and later was minster without portifolio. He resigned from the cabinet of Premier Adolfo Suarez several months ago, partly for reasons of health and partly because his liberal views were not in accordance with those of the government.

He was regarded by malny political leaders as a possible future premier of Spain.

Surivors include his wife, the former Mercedes Areilza, and five children.