Yakov A. Malik, 73 the eloquent and sometimes fiery-tempered diplomat who gained fame during two terms as the Soviet Union's ambassador to the United Nations, died Monday, the official Tass news agency announced yesterday.

The Tass dispatch gave no cause of death, but Mr. Malik is believed to have been in declining health since being injured in an automobile accident on Long Island shortly before his return to the Soviet Union in 1976.

Mr. Malik was ambassador to the United Nations from 1948 to 1952, and again from 1968 until 1976. At the time of his death, he was a deputy foreign minister.

During his first term as ambassador to the U.N., Mr. Malik, on orders from his government, stalked out of a Security Council meeting to protest the presence of Nationalist China. This was the beginning of a six-month boycott of Security Council meetings by the Soviet Union and it led to one of the best-known incidents in the history of the world organization.

For it was during the absence of the Soviet representative that the Security Council voted to send U.N. forces to oppose Communist aggression against South Korea.By reason of the boycott, Mr. Malik was unable to exercise the Soviet Union's right to veto this action.

Mr. Malik was regarded as one of his country's leading experts on the West. During his first term at the U.N., he played a major role in negotiating the terms under which the Berlin Blockade was lifted in 1949.

Mr. Malik left the U.N. in 1953 to begin a seven-year tour as the Soviet Union's ambassador to the United Kingdom.

He returned to the United Nations for the second time in 1968 and became one of the dominant figures there. He was known for the vigorous -- and sometimes abrasive -- way in which he stated his country's views.

He once dismissed a speech by the then U.S. ambassador to the United Nations, Daniel Patrick Moynihan, as a "swan song," noting that Moynihan had recently announced his resignation as ambassador.

On another occasion, he compared the ambassador of the People's Republic of China, Huang Hua, to a "hunchback for whom the only cure is the grave," a jibe based on an old Russian proverb to that effect.

Mr. Malik was born in Kharkov in the Ukraine. He studied economics at the Institute of People's Education there and then graduated from the Soviet Institute for Foreign Affairs at the University of Moscow.

He then went to Tokyo as counselor to the Soviet Embassy. He became ambassador to Japan three years later, serving until the Soviet Union declared war on Japan in 1945.

Mr. Malik had been an alternate member of the Central Committee of the Soviet Communist Party since 1952. He was twice awarded the Order of Lenin and the Order of the Red Banner of Labor.

His son died while Mr. Malik was ambassador to the United Kingdom, and his wife, Valentina, was severely injured in the car accident on Long Island.

In keeping with Soviet tradition in announcing the deaths of high-ranking officials, the Tass announcement yesterday was signed by Soviet President Leonid I. Brehnev, Premier Alexei Kosygin and other members of the Politburo.