Dr. Jacob Haskell Milstone, 64, an authority on blood coagulation, died Thursday at West Haven Veterans Hospital in Connecticut.

He was professor of pathology at Yale University School of Medicine, where he had joined the faculty in 1946.

Dr. Milstone was credited with discovering thrombokinase (factor Xa) and demonstrated that it was a pivotal enzyme that caused blood to clot.

Born in St. Louis, Mo., he was brought here as an infant. He graduated from Central High School, Johns Hopkins College and Johns Hopkins Medical School.

During 1937-40, he was on the faculty of the department of bacteriology at New York University. He then spent two years as a Commonwealth fellow with the Rockefeller Institute at Princeton, N.J.

During World War II, Dr. Milstone served in the Pacific with the Army Medical Corps.

He was a member of Phi Beta Kappa, the Society for Experimental Biology and Medicine, the American Association of Pathologists and Bacteriologists, the American Society for Exploratory Pathology, the American Medical Association and the American Association for the Advancement of Science.

He is survived by his wife, Virginia, of the home in New Haven, Conn.; two sons, Dr. Leonard M., of Hamden, Conn., and Alan D., of New Haven, and his mother, Sadie Mackler Milstone, and a sister, Mrs. Joseph Bieber, both of Washington.