Keyes Beech, who for many years was a foreign correspondent in Asia and won a Pulitzer Prize in 1951 for his reporting on the Korean War, died yesterday of emphysema at Sibley Memorial Hospital in Washington. He was 76 years old and lived in Bethesda, Md.

Mr. Beech (whose first name rhymed with size) covered Asia for five decades, first as a combat correspondent after joining the Marine Corps in 1942. His last post was in Bangkok, where he served as a correspondent for The Los Angeles Times until his retirement seven years ago.

During World War II, he was with the Second Marine Division when that outfit landed at Tarawa, a coral atoll in the western Pacific. He also was the first correspondent to climb to the top of Mount Suribachi on Iwo Jima.

He was often at the front line during the fighting in Korea and was at his best describing the adventures of the Marines in the cold of North Korea and of the American prisoners of war who had been brainwashed by the Chinese.

Years in Vietnam

After the Korean War, he was assigned to Tokyo and reported on all of Indochina. He was in Saigon during the early involvement of the United States in Vietnam. In the mid-1960's he moved to Saigon, and he maintained a residence there until the American departure.

He covered the Vietnam War from the beginning to the end. During the Tet offensive in 1968, he was among the first Americans to see that the offensive was a military victory for the United States and the South Vietnamese, but a political defeat in the United States because of the doubts it raised about American involvement in Vietnam.

James Wallace, a correspondent who covered the war alongside Mr. Beech and who is now senior editor for international news for U.S. News & World Report, praised Mr. Beech as ''highly competitive and extremely professional.''

''He prided himself on being a battlefield correspondent,'' Mr. Wallace said. ''He believed the real story was out where the troops were and not in the briefing room.

''And yet he was always one of the people who in Saigon would help the new kid on the block - a new correspondent just getting started there. Keyes was always very generous when it came to helping others.''

Born in Tennessee

Mr. Beech was born in Pulaski, Tenn., in 1913 and started his newspaper career in St. Petersburg, Fla., as a copy boy. He worked as a feature writer on The Akron (Ohio) Beacon Journal from 1937 until he joined the Marines.

When World War II ended, he became Washington correspondent for The Honolulu Star-Bulletin and later switched to The Chicago Daily News, for which he was the Far East correspondent from 1947 to 1977, covering Japan, China, Korea and Southeast Asia.

His first assignment with The Chicago Daily News was in an area he knew well, Hawaii. He went on to Tokyo, where his political and military analyses drew wide attention.

In 1957, he was among the first group of American correspondents to enter mainland China under Communist rule.

As a result of his colorful experiences he wrote several books, including ''The U.S. Marines on Iwo Jima,'' ''Uncommon Valor'' and ''Tokyo and Points East.''