Merwin Hancock Silverthorn, 88, a retired lieutenant general in the Marine Corps who was a heavily decorated troop leader in World War I, a high staff officer in World War II, and an important contributor to concepts of amphibious assault in the years between, died of cancer Aug. 14 at Bethesda Naval Hospital.

Gen. Silverthorn began his service as an enlisted man in World War I. He finished it in 1954 as commanding general of the Marine Corps Recruit Depot at Parris Island, S.C., the famous installation where Marines enlisted east of the Mississippi undergo "boot camp."

He requested that assignment after serving as assistant commandant of the Corps from 1950 to 1952, a period in which the Marine Corps underwent rapid expansion for the Korean War and in which the rough treatment meted out to recruits at "P.I." was undergoing increasingly critical scrutiny by Congress and the public.

Gen. Silverthorn's purpose was to improve conditions at Parris Island. This concern for the welfare of the men was of a piece with the rest of his career and also with the work he undertook after his retirement. From 1956 to 1957, he was assistant director of defense mobilization in the Office of the President. But after that he devoted full time to the National Prayer Breakfast movement and the International Christian Leaders, of which he was a member from 1959 to 1976 and the president for 10 years.

As a military planner, Gen. Silverthorn was among the small group of Marine officers who developed the doctrine of amphibious warfare in the 1930s. Before World War II, the only large-scale attempt to land on a defended coast in recent times had been the disastrous British campaign at Gallipoli in World War I. Many military theorists considered such operations impossible.

In World War II, tactics and equipment developed by the Marine Corps were factors in proving these skeptics wrong. Gen. Silverthorn made his own contributions to this as an instructor at the Marine Corps Schools at Quantico and in other assignments.

He put his work to use in the early years of the war as the amphibious warfare representative on the small joint staff of the Joint Chiefs of Staff. His expertise came into play not only in setting out broad strategy for the Pacific, but also in planning the war against Germany. This included "Operation Torch," the Army landings in French North Africa in 1942. He also helped found what became the National War College.

In January 1944, Gen. Silverthorn went to the Pacific as chief of staff of what became the Third Marine Amphibious Corps. He took part in the landings on Guam, Peleliu and Okinawa. When the war ended, he was chief of staff of the Fleet Marine Force, Pacific, which included about 400,000 men preparing for the invasion of Japan.

At the outbreak of the Korean War in 1950, Gen. Silverthorn was in charge of Marine Reserves. He was credited with mobilizing them smoothly for active service.

The future general was born in Minneapolis. He attended the University of Minnesota, but left before receiving a degree to enlist in World War I. He received a battlefield commission in France. His decorations included the Navy Cross, the Distinguished Service Cross, two Silver Stars, the Purple Heart and the French Croix de Guerre. He received one Silver Star and the Purple Heart in the battle of Belleau Wood, in which he remained in command of his rifle platoon despite being wounded.

Other decorations and honors included the Distinguished Service Medal and Legion of Merit and the Outstanding Achievement Award from the University of Minnesota.

Gen. Silverthorn lived in Bethesda and attended the Fourth Presbyterian Church.

Survivors include his wife, Marie A. of Bethesda; three sons, Merwin H. Jr., of Kailua-Kona, Hawaii, Russell L., of Del Mar, Calif., and Robert S., of Houston; a sister, Laura Falk of Fort Lauderdale, Fla.; eight grandchildren