The Supreme Court yesterday broadened the power of states to control water resources in federally built conservation projects.

In a 6-3 decision, the court upheld the efforts of California state officials to impose conditions on the use of water in the federal government's New Melones Dam, a part of the California Central Valley Project.

In a separate but related case, the court decided in favor of New Mexico in a dispute with the federal government over diversion of water from the Rio Mimbres River. The court ruled 5 to 4 that the state has primary control over water from the river, which flows through the federal government's Gila National Forest.

In the case before the high court, the California water Resources Board decided that the New Melones Dam, under construction 80 miles southeast of Sacramento, should be only partially filled. This will allow white-water recreation, including fishing and rafting, to contine on the Stanislaus River, from which water will be drawn to fill the dam.

The federal government wanted to fill the reservoir and use the water for additional irrigation projects.

Charles R. Shoemaker, acting director of the California Department of Water Resources, said the decision has implications far beyond the New Melones Dam situation. He said it will enable the state to guarantee releases to preserve water quality in the Sacramento and San Joaquin River Delta area east of San Francisco.

For years, conservationists have been fighting completion of the state's multibillion dollar water project on the grounds that insufficient water would be saved to protect the recreationally attractive delta area from being undermined by saltwater from the Pacific Ocean.

Shoemaker says that it now appears they can guarantee the release of water to preserve water quality as long as congressional guidelines for the use of federal water are met.

The ruling involving the California dam affects 16 other western states including New Mexico.

The others are Arizona, Colorado, Idaho, Kansas, Montana, Nebraska, Nevada, North Dakota, Oregon, Oklahoma, South Dakota, Texas, Utah, Washington and Wyoming.

The majority opinion in the California case, written by Justice William H. Rehnqiust, held that the Reclamation Act of 1902 "clearly provided that state water law would control in the appropriation and later distribution of the water" for federal projects.

The ruling overturned a decision by the 9th U.S. Circuit Court of Appeals that California lacked authority to place conditions on use of the water for the federal dam.

As a result of the Supreme Court ruling, California, even though it has already granted the federal governmnet general rights to the water, may require federal officials to show firm commitments before the water may actually be used. The court sent the case back to the lower courts to determine what conditions California may attach to its water grant.

Yesterday's ruling does not deal with another controversial federal practice that limits sale of water to holders of tracts of land of less than 160 acres.

Justice Byron R. White, in a dissenting opinion joined by Justice William J. Brennan Jr. and Thurgood Marshall, said the majority ruling ran counter to previous interpretations of the Reclamation Act of 1902. White suggested that Congress could straighten out the problem by passing legislation to make it clear state agencies should control spending of federal funds on reclamation projects as well as priorities for the use of water.

In the New Mexico case, private landowners filed suit in 1966 charging the federal government with illegally diverting water from the Rio Membres River for use in the Gila National Forest.