Col. William R. Lawley Jr., who won the Medal of Honor in World War II for flying a crippled bomber with wounded crewmen safely back to England despite his multiple wounds, died on Sunday at a hospital in Montgomery, Ala., his hometown, He was 78.

The cause was complications of pneumonia, his family said.

On the morning of Feb. 20, 1944, the Allies began Big Week, the war's most extensive bombing of Germany's aircraft industry. Among the more than 1,700 planes taking off from England that day was Cabin in the Sky, a B-17 Flying Fortress bomber piloted by Colonel Lawley, then a lieutenant in the 305th Bomb Group of the Army Air Forces.

Lieutenant Lawley was assigned to attack a plant at Leipzig assembling Messerschmitt fighter planes, but a malfunction prevented release of his bombs. As he left the target area, flying at 28,000 feet, 20 German fighters attacked his four-engine plane, which was being flown in combat for the first time.

The shells killed the co-pilot, wounded the other eight crewmen, left Lieutenant Lawley with deep cuts on his face, neck and hands, set an engine ablaze, damaged a wing and sent the bomber into an almost vertical dive.

While bleeding severely, Lieutenant Lawley forced the co-pilot's body off the control column, fought for control of the plane and leveled off at 12,000 feet. Fearing that his plane would explode, he rang a bell signaling his crewmen to bail out but was told that two of them were wounded so badly that they could not use their parachutes.

He lost the help of his flight engineer, who bailed out, but Lieutenant Lawley decided to try to reach England. Although almost five hours of flying over enemy-held territory were ahead of him, he saw no other way to save the badly wounded crewmen.

After extinguishing the engine fire, Lieutenant Lawley avoided German fighters by flying in the clouds. Lieut. Harry Mason, his bombardier, tied the co-pilot's body to his seat back with a parka to keep the already-damaged instrument panel clear, then stood between the two cockpit seats and helped Lieutenant Lawley with the controls.

Having refused first aid, Lieutenant Lawley collapsed from loss of blood and exposure over occupied France. After being revived by Lieutenant Mason, he was finally able to release his bombs, lightening the load and saving fuel, as the plane approached the English Channel.

But as the English coast loomed, with one engine already having burned, a second engine ran out of gasoline and then a third engine caught fire. Lieutenant Lawley was left with only one working engine.

''He was looking for an open pasture,'' Ralph Braswell, one of the plane's two waist gunners, recalled yesterday from his home in Bremen, Ga. ''All of a sudden, there was a Canadian fighter field. He flashed the emergency signal and we went right in.''

All the wounded crewmen survived a crash landing at Redhill, a small fighter strip south of London. The flight engineer who had parachuted out was captured but also survived the war.

The following August, Lieutenant Lawley received the Medal of Honor.

William Robert Lawley Jr., a native of Leeds, Ala., entered flight training in 1942 and went overseas the next year. He was on his 10th bombing mission when attacked by the German fighters, then flew four more missions before being sent back to the United States for a tour promoting the sale of war bonds. He served in the Air Force until 1972, then retired as a colonel.

Colonel Lawley is survived by his wife, Amy; a son, William 3d, of Dallas; two daughters, Susan Decker of Sudbury, Mass., and Anne Sheftic of Dadeville, Ala; a brother, J. D. Lawley of Moody, Ala., and five grandchildren.

After the war, Colonel Lawley kept in touch with the crewmen he saved. Mr. Braswell, the gunner that February day in 1944, visited him recently.

''He had arthritis,'' Mr. Braswell remembered, ''but after I shook his hands, I said, 'They're beautiful. They saved my life.' ''

William R Lawley Jr