Henry Algenon (Al) O'Neal, 59, a retired director of the Navy's Ocean Science and Technology Division who served as project of the pioneering Sealab "man-in-the-sea" experiments in underwter living, died of a heart attack Thursday at a hospital in Greenwood, S.C.

A Navy veteran of World War II, Mr. O'Neal saw duty with a minesweeping group in the Pacific Theater after graduating from The Citadel military college in South Carolina in 1943. Earlier, he had attended Massachusetts Institue of Technology.

In 1957, he was appointed director of Engineering and Applications for the Office of Naval Research. He served as project director of Sealab I and Sealab II, the Navy's first underwater sea-floor laboratories, launched in the mid-1960s, and Project Tektite, a 1969 record-breaking underwater laboratory experiment.

Calling the successful Sealab projects the first steps in achieving economic exploitation of the sea bottom, Navy officials said the experiments proved that man can work on the ocean floor for extended periods of time at depths under high pressure.

Mr. O'Neal received several awards for his work, including two Navy Civilian Career Achievement Awards, the first for Sealab work and the second, at his retirement in 1972, for directing both the Navy's first fully integrated satellite navigator for shipboard use and a scientific project involving oceanographic and meterological studies of the North Pacific.

Before beginning his work with the Ocean Science and Technology Division, Mr. O'Neal worked for the Navy weapons facilities at Patuxent River, Md., and Panama City, Fla.

After retiring, he served as a scientific adviser for the Navy for the clearance of the Suez Canal (1975) and as a consultant for the government of the Palau Island group in the Caroline Islands.

A native of Fairfax, S.C., Mr. O'Neal lived in Arlington moving to Greenwood, S.C., in 1973. He was a part-time physics instructor at a technical college there.

He was a former member of Trinity Presbyterian Church in Arlington and a member of the Marine Technology Society and the American Association for the Advancement of Science.

Survivors include his wife of 35 years, the former Doris Garner, and a daughter, Susan Norman, both of Greenwood; another daughter, Sara Franco of Bamburg, Germany; a son, Navy Lt. Michael O'Neal of Arlington; his mother, Susie B. O'Neal of Fairfax, S.C.; three brothers; one sister and four grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to The Citadel Development Fund, Charleston, S.C.