The city of Greenbelt, which made history in the 1930s as one of the nation's first planned communities and later become a pioneer in cooperative housing, reached another landmark in its history yesterday as its residents celebrated the retirement of the city's 25-year mortgage to the federal government.

The original town of Greenbelt was completed in 1937, as a federal government project to provide low-cost housing for moderate-income families in the New Deal Era. In the late 1940s, residents formed a corporation to purchase the community from the federal government for $6 million.

The sale was closed in December 1952 and the final mortgage payment was made last December. Yesterday, hundreds of the city's residents witnessed the symbolic tearing up of a copy of the community's mortgage by James W. Smith, president of the citizen's corporation. Greenbelt Homes, Inc., and Bruce Bowman, one of the residents who helped from the corporation.

"Greenbelt . . . is not a decaying monument, but a thriving, growing, building community," John Clinton, who supervises the development of new communities for the Department of Housing and Urban Development, told the crowd gathered in Eleanor Roosevelt High School to witness the ceremony.

Greenbelt has remained over the years mostly a community of two-story brick or frame single-family townhouses. Designed to fit the needs of families with children, it has several playgrounds, a community swimming pool, tennis court, and several acres of undeveloped land.

There are about 6,000 residents living in the community. About 100 of them were among the original purchasers of units in the town, according to Ken Kopstein, the community's assistant general manager.

Imogene Byerly, 66, said she decided to settle in Greenbelt in 1942 because of the facilities it offered her two small boys.

Mrs. Byerly's youngest son, Anthony McCarthy, now 34, and an assistant state's attorney in Prince George's County, cited similar reasons for moving back into the community with his wife and two children.

"Greenbelt . . . was designed as a place where you could raise a family in safety and with community care. I enjoyed that when I was growing up there so when it came time for me to raise a family, I couldn't think of a better community environment to reside in," said McCarthy.

When the corporation was formed, Greenbelt homes were selling for $1,500 to $9,000, according to Kopstein. Today, the most expensive home in the community sells for $35,000 Kopstein said. The community is supported through charges the residents pay to the corporation that range from $129 to $240 a month.

Residents pay only for their electricity. All other utilities are paid for out of the monthly charges.

Kopstein said the corporation is planning to develop a renovation program for the community which will consist of insulating many of the homes, replacing windows and shingles, and improving the electrical and plumbing systems.