ROME, April 9— Countess Edda Mussolini Ciano, the eldest daughter and a close adviser of Italy’s Fascist dictator, whose husband was executed after he opposed her father’s rule, died Saturday in a Rome hospital, doctors said today. She was 84.

Countess Ciano had been ill for some time. The cause of death was cardiac arrest related to lung and kidney failure, the doctors said.

She was a close adviser to Mussolini during the 1930’s and was known for her independence at a time when Italian women had few rights.

Her husband, Count Galeazzo Ciano, was Mussolini’s Foreign Minister from 1936 to 1943. In July 1943, however, he voted against Mussolini at a Cabinet meeting that led to the dictator’s arrest and the fall of Fascism.

Under orders from Hitler, occupying German troops freed Mussolini and installed him as head of a puppet government. It found Count Ciano guilty of treason and ordered him executed. Countess Ciano’s pleas to her father and to Hitler were ignored, and her husband was executed by a firing squad in 1944.

After the execution, she disavowed her father and the family name.

“You are no longer my father for me,” she wrote to him. “I renounce the name Mussolini.” After the war, she lived in Rome, then broke her public silence about wartime events in 1975 with a book, “My Testimony.”

She is said never to have reached a reconciliation with her mother, Rachele, who died 15 years ago. Her mother was said to have blamed Count Ciano for Mussolini’s downfall.

The Cianos had three children — Fabrizio, Raimonda and Marzio. She is survived by Fabrizio and Raimonda.•