William (Bill) Armstrong, 70, a swimming instructor at the Ambassador Hotel for more than 30 years, died Tuesday at Northern irginia doctors Hospital after an apparent heart attack.

Mr. Armstrong taught swimming in the hotel swimming pool from 1940 until he retired in 1974. He began to teach there when the Ambassador was the only Washington hotel to have an indoor swimming pool.

He served as a member of the board of governors of the Amateur Athletic Union and was on the public relations staff of the AAU at the 1952 Olympics in Helsinki.

"Everybody in Helsinki and all the world's top athletics will know how to sing the "Star Spangled Banner" now. They had to play it so often at the games nobody could help learning it," he beamed, after returning from that assignment.

In addition to his work with the AAU and as a swimming teacher, he was a member of the Washington Board of Trade, the national board of the Boy Scout of America, the National Press Club, the Masons and Almas Temple.

Mr. Armstrong was a member of the President's Cup Regetta Committee for many years.

After he retired from teaching swimming, he formed American Pool Management, a company that planned and installed large commercial pools.

Mr. Armstrong was born in Pittsburgh. He moved to this area in the late 1930s and studied safety engineering at George Washington University.

He is survived by his wife Olive K., of the home in Falls Church: a daughter LaVerne Moore. of Alexandria: a brother Albert L. of Gambrills. Md., and one grandchild.