Gerard Zinser, the last surviving crewman from the sinking of John F. Kennedy's PT 109 in the South Pacific in World War II, died on Aug. 21 at a hospital in Orange Park, Fla. He was 82.

Mr. Zinser, who lived in Orange Park, had Alzheimer's disease, The Associated Press reported.

In the predawn hours of Aug. 2, 1943, Lieutenant Kennedy's 80-foot Navy patrol torpedo boat was in Blackett Strait in the Solomon Islands, about 800 miles north of Australia. The 26-year-old skipper and the 12 crewmen were hoping to sink a Japanese warship to support the invasion of New Georgia Island.

Mr. Zinser, a machinist's mate first class and the only career Navy man in the crew, was standing on the starboard side of the deck, near the engine-room hatch, when the patrol boat was sliced in two.

''I was right around midships,'' he remembered in an interview long afterward, ''and I heard shouting going on. 'Ship at 2 o'clock!' ''

It was the Japanese destroyer Amagiri.

''Our watches couldn't see the ship until it was right on top of us, hitting us starboard-side amidships,'' Mr. Zinser recalled. ''I was hurled into the air. I was unconscious 10 to 15 minutes. When I came to, I was in the water. There were small fires. The front part of the boat stayed afloat. The stern, where the engine room was, sank immediately.''

Two crewmen were killed in the ramming, Kennedy suffered an injury to an already weakened back, Mr. Zinser was burned on the arm and chest, and an engine-room crewman, Machinist's Mate Patrick McMahon, suffered severely burned hands.

The sailors abandoned the bow and headed for tiny Plum Pudding Island, three and a half miles away. Kennedy, swimming the breast stroke, towed Seaman McMahon on his back, grasping the strap of the man's life jacket in his teeth. The nine other survivors swam together, holding onto a 2-by-8-foot plank from their boat. It took the 11 men four hours to reach the island. The crewmen, who later swam to a slightly larger island in search of food, were stranded for six days, living off coconuts, before they were rescued.

Kennedy buoyed the spirits of his men and carved a distress message into a coconut that he gave to two islanders who helped bring about the rescue. His actions in the episode created a heroic image that aided his emergence on the national political scene. The story was told in the journalist Robert Donovan's book ''PT 109'' (McGraw-Hill, 1961) and in the movie with the same title two years later, starring Cliff Robertson as Kennedy. PT 109 tie clasps became a trademark of the Kennedy people.

Mr. Zinser, a native of Belleville, Ill., who had joined the Navy in 1937, retired 20 years later as a chief petty officer, then became a mailman in Florida.

On Jan. 20, 1961, Mr. Zinser and seven fellow crewmen rode in the Kennedy inaugural parade on a float replicating PT 109.

When Mr. Zinser learned that Kennedy would appear at a fund-raiser for Senator George Smathers of Florida at a Miami hotel the next year, he and his wife bought tickets.

As his son, Mark, told it: ''My dad was worried, because they weren't young sailors anymore, and he said to my mom, 'He won't even recognize me.' So my mom told him how to introduce himself. He grabbed the president's hand and said, 'Zinser, Gerard E., motor machinist's mate first class, reporting for duty. PT 109' -- just the way he had first introduced himself when he came aboard.''

Mark Zinser said Kennedy embraced his father and they started to talk, but aides soon hustled the president away to meet other well-wishers.

Mr. Zinser was an extra in the movie ''PT 109,'' which opened in June 1963. He attended Kennedy's funeral five months later.

In addition to his son, Mr. Zinser is survived by seven daughters, Jerilyn Dill, Carolyn Pickard, Patricia Vriesenga, Rosemary Shiflet, Pamela McLin, Marcia Cristell and Margaret Zinser, 24 grandchildren and 10 great-grandchildren.

In 1994, when he appeared at the opening of an exhibition observing the 50th anniversary of D-Day at the Kennedy library, Mr. Zinser remembered how his former skipper rallied the crewmen and towed the badly burned sailor to shore.

''I served 20 years in the Navy,'' he said then, ''and I never had an officer that would ever come close to what I saw Kennedy do.''

Photo: Gerard Zinser, third from right, with crew members, and the float they rode in the Kennedy inaugural parade. (From ''PT 109,'' Robert J. Donovan/McGraw-Hill)

Gerard Zinser (1918)