In a decision expected to have far-reaching effects on the land-use planning process throughout Maryland, the state's Court of Appeals yesterday upheld Montgomery County's right to implement a detailed land-use plan for the Friendship Heights area that significantly limits future growth there.

The unanimous ruling, written by the chief judge of Maryland's highest court, was called "one of th emost important land-use decisions made in this country in the past 20 years" by Royce Hanson, chairman of the Maryland-National Capital Park and Planning Commission.

In effect, the decision allows local authorities broader discretion to make land-use decisions based on the specific impact that future development would have on such public facilities as streets and sewers.

"We think the record in this case fully supports (the contention) that the rezoning was designed to control the use of land and buildings . . . so as to accomplish the most appropriate use of land, consistent with the public interest . . ." Chief Judge Robert C. Murphy wrote in the opinion.

". . . The rezoning was comprehensive and bore a substantital relationship to the public health, comfort, safety, convenience, morals and general welfare," the opinion continued.

As well as affirming the county's right to impose the zoning, the court overturned a 1976 ruling by a Montgomery County Circuit Court judge who had agreed with the planning objectives but who found that the procedures used to implement them were unfair to area property owners.

The court's decision is a victory for many residents of Friendship heights who, even more than county planners, wanted to slow the pace of development, which over the last 15 years transformed the 42-acre village just northwest of Western and Wisconsin Avenues into a mini-Manhattan of high-rise office and apartment buildings.

"The citizens are greatly relieved to know that the courts have sustained the power of the county to control development," said Norman Canoff, a representative of the 16 local citizen groups that had fought for the down-zoning proposal.

Under the Friendship Heights land-use plan, about 24 acres of land in the area were put in more restrictive zoning categories than had previously applied.

These new zones, all part of an overall zone called a Central Business District, establish a complex formula restricting the total floor area of new buildings based on the size of the lots on which they are built.

This formula has the effect of the limiting either the height of a new building, or the area of ground it can cover, or a little bit of both, depending on the builder's preference.

The concept of central business district zones evolved over the past 10 years as Montgomery County planners set about to revitalize some of the decaying downcounty urban areas like Silver Spring.

The planners also wanted to centralize high-density urban development in specific areas like Friendship Heights, Bethesda, and Silver Spring, locating these urban centers around the new stations of the Metro's rapid rail system.

At the same time these plans were developing. Friendship Heights was changing from a suburban area of 400 people into a high-rise island of more than 3,000.

Commercial giants such as Saks Fifth Avenue and Woodward & Lothrop moved into the area, feeling the dreams of developers who envisioned Friendship Heights as a "gateway center" to the nation's capital.

It was Woodward & Lothrop's plan to replace it's Friendship Heights store with a new, larger one - and, in the process, build a massive "Town Center" mall complex on its 8-acre triangle of land - that triggered the chain of events that led to yesterday's decision.

In the course of the five-year fight, during which the store and developers of the proposed complex alleged there was a conspiracy among local government authorities to thwart their plans, dozens of individuals, groups and agencies joined the case on both sides.

Nearly 5,000 pages of information and arguments were filed during the three-year legal battle that followed the two years of planning debates.

A total of three cases were ruled on yesterday by the courts - Woodie's suit trying to overturn the county's zoning decision, a suit by TKU Associates, who would have developed the "Town Center," against the Washington Suburban Sanitary Commission, which did not grant a sewer connection for the project, and another TKU suit against the county.

In all three cases, the decisions went against Woodward & Lothrop and TKU.

Stephen Z. Kaufman, an attorney for some of the Friendship Heights property owners who had fought the countys zoning decision, said yesterday that the decision "just means that the private property owner has that much less say about how his land is used."