The Supreme Court ruled unanimously yesterday that zoning and land use laws to protect open space do not violate the rights of private property owners.

The ruling was a defeat, though limited, for developers and landowners around the country who have been challenging environmental restrictions as unconstitutional seizures of their property rights.

Donald and Bonnie Agins, a California couple who bought scenic property overlooking San Francisco Bay hoping to build five houses there, brought yesterday's case. After they purchased the land in 1968, the city of Tiburon, Calif., imposed new open space zoning on the property, requiring the owners to develop environmental impact statements and master plans before the city would even consider their building plans.

The Agins, contending that the action stripped the property of its value, never submitted their building application and instead went to court demanding $2 million in compensation from Tiburon.

A Supreme Court victory for the Agins, environmentalists feared, would have paralyzed land use planning by confronting governments with the threat of massive compensation demands from landowners.

But because the Agins never applied for permission to build, the justices declined to rule on a crucial question: Does a total or partial ban on development in such situation violate the Constitution, and if so, must governments compensate the land-owners or must they just change the zoning?

Environmentalists did regard yesterday's ruling as a two-pronged victory, however. The justices ruled for the first time that open space laws "advance legitimate governmental goals." That determination is the first step in justifying legally an otherwise impermissible restriction on constitutional rights and should be helpful to environmental lawyers in future battles with developers.

Tiburon's zoning regulations "are exercises of the city's police power to protect residents from the ill effects of urbanization," Justice Lewis Powell wrote for the court. "The zoning ordinances benefit [the Agins] as well as the public by serving the city's interest in assuring careful and orderly development of residential property with provision for open spaces."

The justices also left untouched the much broader triumph for environmentalists contained in the California Supreme Court's ruling in the Agins case. The California court ruled that even if the Agins rights were violated, the remedy could never be compensation but only invalidation of the zoning law.