Jerrold R. Zacharias, 81, a nuclear physicist and educator whose ideas led to a reformation and simplification of the teaching of physical sciences in American high schools, died July 16 at his home in Belmont, Mass. He had a heart ailment.

Dr. Zacharias, who retired from the faculty at the Massachusetts Institute of Technology in 1970, also had been director of the engineering division of the Manhattan Project, which developed the first atomic bomb during World War II.

As director of MIT's Laboratory of Nuclear Science after the war, he designed the world's first atomic clock. Earlier he had been part of a team of scientists that developed a radar system for the Navy.

But his greatest impact on American science came in the teaching reforms that resulted from his ideas. During the 1950s, Dr. Zacharias became increasingly dissatisfied with the way science was being taught, contending that students were too often being given "unrecognizable melanges of dull facts and bad technology under the name of physics or chemistry." He called on the scientific community to develop textbooks and curricula that would make science interesting and understandable to students.

In 1956 he formed an organization called the Physical Science Study Committee, which set about developing such a program, and over the next two decades most of Dr. Zacharias' ideas were incorporated into high school science curricula.

He believed that students could learn principles of science from simple and easily performed experiments, and that even elementary school students were not too young to benefit from this method of instruction. He was also a firm believer that one of the most effective ways of learning was for students to teach other students. In this relationship, he argued, the pupil playing the role of teacher would benefit as much as the pupil playing the role of student.

He wanted students to understand that scientific research and discovery involved many more failed experiments than successful ones, and he criticized most standard textbooks for failing to record the months and years of failure and frustration that preceeded most successful experiments.

During the 1960s and 1970s, Dr. Zacharias chaired and served on several educational advisory and study committees, including a presidential Panel on Educational Research and Development in the early 1960s. Among that group's recommendations was the creation of model subsystems in deprived areas of large urban school districts. That recommendation was followed in several cities around the nation, including Washington, with mixed results.

Born in Jacksonville, Fla., Dr. Zacharias graduated from Columbia University, where he also earned his doctorate. He taught at Hunter College and did research in the molecular beam laboratory at Columbia until 1940, when he went to MIT to head the division of radar transmitting components at the radiation laboratory.

He is survived by his wife, Leona Zacharias of Belmont; two daughters, Susan Zacharias of San Diego, Calif., and Johanna Zacharias of Baltimore, and three grandchildren.