Archibald Bulloch Roosevelt, 85, who was the last surviving son of President Theodore Roosevelt and a decorated combat veteran of both world wars, died Saturday in the Stuart Convalescent Center in Stuart, Fla., where he had been hospitalized following a stroke several months ago.

As a company commander in the American Expeditionary Force in France during World War I, he was wounded three times. The then-Capt. Roosevelt received the French Croix de Guerre for this service. t

During World War II he reenlisted in the Army and served as a lieutenant colonel in the 41st Infantry division's 162nd Regiment. The regiment spent 76 consecutive days of combat in New Guinea jungles. Col. Roosevelt became a hero to fellow officers and men when he continually drew enemy fire to pin-point Japanese artillery positions.

As an Army private told an Associated Press reporter during the 1942 ordeal, "Col. Roosevelt stood up with a map in his hand and every time a gun fired he jotted down its position."

"They fired at us for half an hour," the private went on, "barely missing us several times . . . Col. Roosevelt was standing there deliberately encouraging them to fire at us."

"The next day our artillery landed squarely on those guns and the Japs never fired them again. That was when their resistance ended -- and Col. Roosevelt should get most of the credit for that final blow," the soldier said. In conclusion, the private mused that "Roosevelt's a good officer, but he's got too damn much guts."

During his World War II service he was again wounded, suffered from malaria, and was awarded both the Silver Star Medal with oak leaf cluster and the Purple Heart Medal.

Like his father, he was an outdoorsman who loved hunting and fishing. He joined the Boone and Crockett Club in 1922, a conservation organization started by President Theodore Roosevelt, and after World War II served as the organization's secretary, vice-president and finally, president. He was named honorary President for life in 1963.

Mr Roosevelt also had been a trustee of the New York Zoological Association, treasurer of the Long Island Nature Conservancy, and a member of the American Committee of the World Wildlife Fund.

A New York investment banker by profession, he first had worked for the Wall Street firm of Roosevelt & Sons, and later took charge of the tax exempt bond business at Roosevelt & Weigold. In 1946 he helped found Roosevelt & Cross, and recently had served on the board of the Hobe Sound National Bank in Florida.

Mr. Roosevelt was born in Washington while his father was serving as U.S. Civil Service Commissioner. He attended Groton and was a graduate of Phillips Andover Academy and a 1917 graduate of Harvard University. He had retired to Hobe Sound, Fla., after maintaining homes in New York City and Cold Spring Harbor, Long Island.

His wife, the fromer Grace Lockwood, died in 1971.

Mr. Roosevelt is survived by a son Archibald B. Jr., of Washington; three daughters, Edith Kermit Roosevelt, of Washington, Theodora Rauchfuss, of Patterson, N.C., and Mrs. William E. Jackson, of New Yor City; a sister, Alice Roosevelt Longworth of Washington; seven grandchildren, and one great-grandchild.

The family suggests that expressions of sympathy be in the form of contributions to the Boone and Crockett Club Conservation Fund, c/o the Secretary, 424 North Washington St., Alexandria, 22314.