Bill Downs, 63, a network correspondent for the American Broadcasting Co. in Washington for the past 15 years, died Wednesday of cancer at Suburban Hospital in Bethesda.

Mr. Downs, whose most recent assignment with ABC was to cover ecology and matters on natural resources, began his broadcast career in 1942 with the Columbia Broadcasting System in London during World War II.

His wartime assignments included Moscow, where he was stationed from 1942 to 1944, and where he covered the battle of Stalingrad, the D-Day landings in Normandy, the surrender of German forces to Field Marshall Montgomery, and the surrender of Japan.

He later covered the atomic tests at Bikini Atoll in 1945, the Soviet blockade of Berlin and the resulting Oerlin Airlift, the Korean conflict, and numerous stories in the Unites States, including presidential campaigns. He was assigned to Rome by CBS from 1953 to 1956, and then became a specilist in diplomatic reporting.He resigned from CBS in 1962.

Mr. Downs joined ABC after a brief period of free-lance writing. He helped cover events surrounding the assassination of President John F. Kennedy. He was ABC's correspondent at the Defense Department from 1963 until 1970, when he switched to ecology.

His prizes included a National Headliner's Club award for his exclusive coverage of the German surrender to Montgomery and and Overseas Press Club citation in 1949.

William Randall Downs Jr. was born in Kansas City, Kan. He grew up there and graduated from University of Kansas in 1937. He worked for Kansas City newspapers and then joined the old United Press in that city. UP, now United Press International, transferred him to London in 1940.

Mr.Downs' survivors include his wife of 31 years, the former Rosalind Gerson, of the home in Chevy Chase; three children, william R. III, of Flagstaff, Ariz., Karen Louise Smith, of Portland, Ore., and Adam Michael, of Silver Spring; his parents, William R. Sr. and Katherine Tyson Downs, and a sister, Bonnie Shoults, all of Kansas City.

The family suggests that expressions of sympthy be in the form of contributions to a charity of one's choice.