V.K. Wellington Koo, 97, who as Nationalist China's leading diplomat during the first half of this century served as his country's ambassador to Great Britain during World War II, as its ambassador to the United States in the postwar years, and as its chief delegate to the first assembly of the United Nations, died of a heart ailment Nov. 13 at his apartment in New York City.

Dr. Koo's career in diplomacy spanned more than four decades, and it reflected much of the history and development of China from the revolution led by Dr. Sun Yat-sen in 1911 to the Communist victory over Generalissimo Chiang Kai-shek on the mainland of China in 1949. Not only was he one of the last great figures of that time and place, but he also retained his stature despite the fact that many of the causes he defended ultimately were lost.

In 1919 he was China's plenipotentiary to the Paris Peace Conference ending World War I. In that capacity it was his responsibility to refuse to sign the Treaty of Versailles because the allied powers wanted to give Germany's former possessions in China's Shantung Province to Japan.

He was the chief Chinese delegate to the League of Nations in 1920, and he served as the Chinese representative to the League's Commission of Inquiry into the Japanese incursion into Manchuria in 1931 that ultimately led to one of the major conflicts of World War II.

To no avail, he pleaded China's cause against Japan before the League and the Nine-Power conference in Brussels after Japanese troops exhcanged fire with Chinese troops at the Marco Polo Bridge near Peking in 1937, the incident that triggered Japan's invasion of China proper.

He was China's ambassador to France in June 1940, when Paris fell to the Germans, and he left with the French government, which set up temporary headquarters at Tours and later in Vichy. In 1941, he was sent to London as ambassador. He served there until 1946, when he was appointed ambassador to the United States.

During 10 years in Washington, Dr. Koo was an outspoken critic of the communist government in China, which he accused of attempting to blackmail the United States into diplomatic concessions by holding American prisoners from the Korean conflict. He also repeatedly assailed the government on the mainland for what he termed "feverish military aggression," which he said was aimed at "destroying the basic virtues of the Chinese people."

In 1957 the U.N. General Assembly and Security Council elected Dr. Koo a judge on the International Court of Justice, where he served for 10 years before retiring as vice president of that body. Since then he had resided in New York and had served as an adviser to the president of the Republic of China.

Dr. Koo was born in Shanghai on Jan. 29, 1888, the third son of a prosperous merchant. He came to the United States in 1904 and attended school here for two years before enrolling in Columbia University. He earned bachelor's and doctoral degrees at Columbia. He was as fluent in English and French as he was in Chinese.

In 1912 he returned to China and served as secretary to Yuan Shih-kai, the first president of the entire country after the Republic of China was established in 1911. He served as minister to Mexico and then to the United States during World War I. During the 1920s he was China's minister of foreign affairs and then acting prime minister. He negotiated the resumption of diplomatic relations between China and Russia that had been severed at the time of the Russian Revolution in 1917.

Dr. Koo's first wife, May Tong Koo, died in the influenza epidemic of 1918. His second marriage, to Huilan Oei Koo, ended in divorce.

Survivors include his wife, Juliana, of New York City; two children from his first marriage, Teh-Chang Koo and Patricia Koo Tsien; three stepdaughters, Genevieve Young, Shirley Young Krandall and Frances Young Tang; 19 grandchildren, and two great-grandchildren.