The Supreme Court, in a 9-to-0 ruling, yesterday upheld a state's power to limit prices for intrastate natural gas in the face of nationwide price deregulation.

The justices said that a 1979 Kansas law legitimately blocked certain natural gas producers in the state from collecting windfall profits, saving state consumers an estimated $128 million on their gas bills over five years.

Oklahoma has a similar law, and estimates are it will save its utility users $1 billion over several years. The high court ruling also could spur other states to try natural gas price regulation.

The laws prohibit gas producers from raising rates for intrastate fuel being sold under existing long-term contracts up to the higher price levels allowed after Congress began deregulating natural gas in 1978.

Justice Harry A. Blackmun, writing for the court, rejected arguments by Energy Reserves Group Inc. that the law was unconstitutional because it interfered with the gas producer's private contract with a utility.

In addition, six of the justices took a strong stand for states' "police power to protect consumers from the escalation of natural gas prices caused by deregulation."

Chief Justice Warren Burger and Justices Lewis F. Powell Jr. and William H. Rehnquist limited their votes to the contract issue.

In two other business-related cases, the court made it easier for private investors to win a lawsuit charging stock fraud and struck down a Tennessee bank tax that the justices said discriminates against financial dealings with the federal government.

In the stock fraud case, the court, in an 8-to-0 decision, said that investors need only "prove that it is more likely than not that they were defrauded" in order to recover damages under a frequently used section of the 1934 Securities and Exchange Act. The decision overturned a lower court ruling that investors must show "clear and convincing" evidence to recover damages.

In the Tennessee case, banks doing business in the state had to pay local governments 3 percent of their net earnings on federal financial obligations, minus a portion of their property taxes. But no taxes were charged on income from bonds or securities issued by the state or local governments.