Paul Davidoff, an influential planner who was instrumental in challenging suburban zoning regulations that exclude low-income people, died yesterday at the Memorial-Sloan Kettering Cancer Center of complications resulting from treatment for cancer. He was 54 years old and lived in Brooklyn.

Mr. Davidoff, who combined his expertise as a lawyer and planner with a crusading spirit, founded the Suburban Action Institute in 1969 and served as its executive director until 1982.

The institute mounted a number of legal attacks against exclusionary zoning in New York, New Jersey and elsewhere and its work was absorbed in other suits. The most notable suit, against the Philadelphia suburb of Mount Laurel, N.J., resulted in two decisions by the New Jersey Supreme Court requiring communities across the state to create zones for low- and moderate-income housing.

In recent years, he was named a professor of urban planning at Queens College and essentially brought the institute there with him under its new name, the Metropolitan Action Institute. In this role, he worked to limit the impact of neighborhood gentrification on low-income people in New York City. Dropped Out of Law School

He often served as a consultant or expert witness in housing cases, including one involving racial quotas at Starrett City in Brooklyn, and wrote many articles encompassing his theories.

Mr. Davidoff, a man of imposing build and strong voice, was born in Queens. He attended the Little Red Schoolhouse and Elizabeth Irwin High School in Greenwich Village, and graduated from Allegheny College in Meadville, Pa. in 1952.

He entered Yale Law School, but, engaged by a planning course he took, he dropped out and enrolled in the University of Pennsylvania's School of Planning and Architecture, from which he graduated in 1956. While teaching at Pennsylvania, he completed his law degree in 1961.

He began his career as a planner for the town of New Canaan, Conn. whose zoning regulations the institute would later challenge. He also worked as a planner for the architectural firm of Voorhees, Walker, Smith & Smith.

In 1964, he founded the urban studies department at Hunter College and taught there until 1969, when he founded Suburban Action.

He leaves his wife, Linda; two daughters, Susan, 28, and Carla, 23, both of Brooklyn; two sons, Daniel, 16, and Thomas, 13, both at home; his mother, Mildred, of Manhattan; and his brother, Jerry, of Westport, Conn..

Plans for a memorial service on Sunday were incomplete yesterday.