Leon Henderson, a leading New Deal economist who became the first director of the Office of Price Administration, which was established to curb inflation in World War II, died Sunday at the Tri-City Medical Center in Oceanside, Calif. He was 91 years old and lived in Carlsbad, Calif.

After being named O.P.A. administrator in the Roosevelt Administration in 1941, Mr. Henderson, one of the first advocates of price ceilings in war mobilization, undertook to establish a ceiling on goods ranging from agricultural products to jewelry. He remained with the agency through 1942, when he resigned to become an economic commentator and consultant.

David Ginsburg, a Washington lawyer who was general counsel to the agency, said yesterday that Mr. Henderson had made a special contribution to the country in World War II because he alone understood the scope of what the economy had to produce to mobilize for war. Mr. Henderson used this knowledge, Mr. Ginsburg said, to help convince the nation that the vast economic mobilization could be accomplished.

Mr. Henderson joined the Roosevelt Administration in 1934 when he was appointed as a consumer adviser in the National Recovery Administration, which was formed to help industrial recovery in the Depression. Rise in Roosevelt Era

But he was an outspoken critic of N.R.A. policies. His criticisms caught the sympathetic attention of Gen. Hugh S. Johnson, a key New Dealer who was the the agency's first administrator. General Johnson promoted Mr. Henderson to the post of director of the agency's research and planning division.

Mr. Henderson's standing within the Administration was greatly enhanced when he predicted the 1936-37 boom and the 1937 recession. He developed his predictions after careful analyses of consumption. His motto was, ''Keep your eye on the consumer.''

After basic N.R.A. industrial policies were invalidated by the Supreme Court in 1935, Mr. Henderson became secretary to the Senate Committee on Manufactures. He was the economist for the Democratic National Committee in the 1936 Presidential campaign.

After that campaign he went back to work for the Goverment as economic counselor to the Works Project Administration under Harry Hopkins, another key Roosevelt aide, and in 1938 became secretary of the Temporary National Economic Committee, a Congressional panel. The committee has been credited by historians with the most thorough examination ever made of monopolies in the United States.

In April 1939, Mr. Henderson was appointed to the Securities and Exchange Commission, succeeding William O. Douglas, who had been appointed an Associate Justice of the Supreme Court. Key Role in Wartime Posts

Also in 1939, when the advisory panel to the National Counsel on Defense was established, Mr. Henderson was one of its seven original members.

In 1941 he was given one of the Administration's toughest jobs, administrator of the new Office of Price Administration, and he became a national figure.

Mr. Henderson was born in Millville, N.J., where his parents had a farm. He was working his way through Swarthmore College when he left to join the Army in World War I. He started as a private in the Ordnance Department and worked up to captain with the War Department and the War Industries Board in Washington.

After the war he returned to Swarthmore, graduating in 1920. After graduation, he taught at the Wharton School of the University of Pennsylvania and at the Carnegie Institute of Technology, now Carnegie-Mellon University.

From 1923 to 1925, he was Deputy Secretary of the Commonwealth of Pennsylvania in the administration of Gov. Gifford Pinchot, and was also director of accounts, state personnel officer and secretary of the state employment service.

From 1925 to 1934, when he joined the N.R.A., Mr. Henderson was director of the remedial loan division of the Russell Sage Foundation in New York, which focuses on sociology research. His foundation studies on consumer credit and investigations of loan sharking helped obtain the passage of legislation in several states against usurious interest rates.

Mr. Henderson is survived by his wife, the former Myrlie Hamm; two daughters, Lynn H. Clark, of Rehoboth Beach, Md., and Beebe H. Castro, of Shady Side, Md.; a son, Leon Jr., of Rocky Mount, N.C.; a sister, Nellie Stadler, of Carlsbad, seven grandchildren and three great-grandchildren.