Retired Navy Rear Adm. William B. Fletcher Jr., an authority on amphibious warfare who was a decorated combat veteran of World War II, died Saturday at the Bethesda Naval Hospital. He had pneumonia and congestive heart failure.

Adm. Fletcher was commanding officer of the tanker Netches when World War II began. After the Netches was sunk at the battle of Midway, Adm. Fletcher became commander of the attack transport Libra and took part in the battle for Guadacanal in the Solomon Islands in the Pacific.

He participated in a number of other amphibious landings and served as chief of staff of Amphibious Group 4 in the Atlantic before the end of the war.

His decorations for the war included the Silver Star Medal, the Bronze Star Medal, and the Legion of Nerit, all with Combat V.

His post-war assignments included tours in London and Washington. While serving here in the mid-1940s, and again for two years before retiring from active duty in 1960, he served on the staff of the chief of Naval Operations and also wrote Navy tactical manuals on amphibious warfare.

After retiring from the Navy, Adm. Fletcher remained in this area. He moved to Annapolis in 1966 and then to Blue Ridge Summit, Pa., in 1973. He was supervisor of the technical writing division of Vitro Laboratories in Silver Spring before retiring a second time in 1965.

Adm. Fletcher was a son and a grandson of Navy flag officers. A grandfather, Adm. Peter C. Asserson, had helped establish the Navy's civil engineer corps, and his father, Rear Adm. William B. Fletcher Sr., was an 1882 graduate of the U.S. Naval Academy at Annapolis and commanded U.S. Naval forces in Brest, France, during World War I.

Retired Rear Adm. William B. Fletcher Jr. had two brothers, Navy Lt. Comdr. John A. Fletcher and Navy Cmdr. Paul W. Fletcher, both of whom died while on active duty.

Adm. Fletcher was a native of Lynn, Mass., and a 1921 graduate of the U.S. Naval Academy at Annapolis, where he was an intercollegiate gymnastics champion. He also earned a master's degree in engineering at Columbia University.

Before World War II, he was a member of the Navy Submarine Service and commanded one of the early subs, the 0-7. He also served as executive officer and commander of destroyers during the 1930s.

Adm. Fletcher's first wife, Louise Littlepage Fletcher, died in 1963. Survivors include his wife, Geraldine F., of Blue Ridge Summit; a son by his first marriage, retired Navy Cmdr. William B. III, of Alexandria; a stepdaughter, Carolyn L. Pearce of Alexandria; a stepson, Thomas P. Littlepage of Ballstn Spa, N.Y., and a sister, Mary Louisa Fletcher of Orrs Island, Me.

The family suggests that expressions of sympathy be in the form of contributions to the Naval Academy Athletic Association in Annapolis.