Lynn H. Herring, assistant chief of the U.S. Park Police, yesterday was named chief of the 566-member law enforcement agency.

Herring, who will be 51 on Christmas Day, succeeds Parker T. Hill, who retired in September. A veteran of 20 years of Park Police service, Herring had been acting chief since then.

As chief, Herring will command a force assigned to more than 50,000 acres -- about 80 square miles -- of National Park Service land, monuments, memorials and parkways in the Washington metropolitan area and on its outskirts.

Herring joined the Park Police in 1961 as a patrolman, and went on to serve in the communications and records branch. In 1967, he was promoted to sergeant, and subsequently was assigned to the Park Police academy as a training supervisor.

Other assignments included service as personnel officer and recruiting sergeant and as field commander in the operations division in 1970 and 1971. He was promoted to lieutenant while in the operations division.

Named a major in 1974, he was responsible for setting up the first Park Police field office in the Golden Gate recreation area, and then was made first commander of the San Franciso field office. He returned here in 1978 to become deputy chief of administrative services, and in March, 1980 became assistant chief of the force.