Dr. Harry Stephen Ladd, 82, a retired paleontologist with the U.S. Geological Survey and an authority on coral reefs of the Pacific, died Nov. 30 at the Carriage Hill nursing home in Bethesda. He had Parkinson's disease.

Dr. Ladd was born in St. Louis and graduated from Washington University there. He took master's and doctor's degrees at the University of Iowa and then made his first trips to the islands of the Pacific. He spent two years mapping the geology of two islands of the Fiji group.

He later taught at the University of Virginia, worked for an oil company in Venezuela and studied Fijian fossils at the Smithsonian Institution and the University of Rochester. In 1936, he joined the National Park Service and was assigned to Atlanta and Richmond.

Dr. Ladd began his career at the Geological Survey in 1940. From 1942 to 1945, he was the agency's regional geologist in Rolla, Mo. He then settled in the Washington area.

After World War II, he established the Pacific Island Mapping Program, a joint venture of the Survey and the Corps of Engineers. He took part in the survey of Bikini Atoll in the Marshalls prior to the atomic and hydrogen bomb tests there. He also organized a series of deep drillings on various atolls to provide a more complete picture of their structure. This led to Project Mohole, a core hole that was drilled in 11,700 feet of water. Similar work continues with the Deep Sea Drilling Project of the National Science Foundation.

In the late 1950s, Dr. Ladd was assistant chief geologist of the Survey. In 1950, he returned to full-time research on the paleontology of the Pacific islands. He retired in 1969, but continued as a research associate until 1978.

Dr. Ladd was a fellow and a former vice president of the Geological Society of America, a vice president of the American Association for the Advancement of Science and a president of the Paleontological Society and the Geological Society of Washington. He was a member of the Cosmos Club.

He received the Distinguished Service Award of the Interior Department in 1965 and the Paleontological Society Medal in 1981.

Survivors include his wife, the former Jane Mahler, of Chevy Chase; two sons, Nicholas, of Philadelphia, and David, of Cambridge, Md., and four grandchildren