Dr. Kalman Laki, 74, an authority on blood clotting at the National Institutes of Health and a senior research professor in the department of chemistry at American University, died Feb. 12 at Fairfax Hospital after a heart attack.

Dr. Laki, a biochemist, joined the staff of NIH in 1948 as a visiting scientist. He became the chief of the Laboratory of Biophysical Chemistry at what is now the National Institute of Arthritis, Diabetes, Digestive and Kidney Diseases. In 1970, he left that post and was named chief of the laboratory's section of physical biochemistry. He held that position until his death.

In 1973, he received the J. F. Mitchell Foundation Award for the discovery of Factor 13, an agent that strengthens blood clots and prevents bleeding. He also received the Kossuth Award, given by Hungary for science. In 1976, he was made an honorary doctor of medicine by the University of Debrecen in Hungary.

Dr. Laki was born in Szolnok, Hungary. He earned a doctorate in chemistry at the University of Szeged. He came to the United States in 1947 and settled in Bethesda in 1948.

He was the editor of three books and the author or coauthor of more than 150 scientific papers. He was a regional director and advisory director of the National Foundation for Cancer Research and a member of the American Society of Biological Chemists, the Washington Academy of Sciences and the Hungarian Academy of Sciences.

Survivors include his wife, Elizabeth, and a son, George, both of Bethesda, and a brother, Arno Laki, and a sister, Iren Nagy, both of Hungary.