The Supreme Court yesterday struck down portions of liquor price control laws in 21 states, ruling that such laws unconstitutionally restricted interstate commerce.

The 5-to-3 ruling involved a New York law requiring distillers to pledge that the prices they charged New York wholesalers were as low as those charged that month in any other state.

A liquor distiller, joined by winemakers and brewers, challenged the law, arguing that it was unconstitutional because New York made it illegal for a distiller to reduce its price in any other state during that 30-day period. New York's law, in conjunction with those in other states, in effect created a national uniform pricing law, opponents argued.

Justice Thurgood Marshall, writing for the court in Brown-Forman Distillers v. New York State Liquor Authority, agreed.

"While a state may seek lower prices for its consumers," Marshall said, "it may not insist that producers or consumers in other states surrender whatever competitive advantages they possess."

The "proliferation" of similar state laws after a 1966 Supreme Court ruling allowing them, Marshall said, "has greatly multiplied the likelihood that a seller will be subjected to inconsistent obligations in different states."

The ruling directly involved laws in 21 states, including Maryland, and cast doubt on similar provisions in 18 other states, including Virginia, which buy liquor directly from distillers.

Attorneys involved in the litigation said it is unclear what effect yesterday's ruling will have on prices and predicted further litigation on related issues.

Arnold M. Lerman, an attorney for the Wine Institute, said laws in the 18 states purchasing directly "are still a clog on the market" and that a wide variety of state regulations on liquor, such as those on retail prices or advertising, were not affected.

"Nobody can say whether there will be higher or lower prices," Lerman said, "but you will have much more of a free market in determining prices and that would mean higher prices in some areas and lower prices in others."

The court came close to, but did not, overrule the 1966 ruling in Seagram & Sons Inc. v. Hostetter, which involved essentially the same New York law. Justice Harry A. Blackmun, concurring yesterday, said the 1966 decision was "now a relic of the past. It was decided when [similar pricing laws] were comparatively new and long before the proliferation of overlapping and potentially conflicting. . . statutes that has taken place in the last two decades." Blackmun said the court should "face reality and overrule" the prior case.

Justice John Paul Stevens, joined by Justices Byron R. White and William H. Rehnquist, dissented, saying that there is no evidence that New York's law had affected Brown-Forman's prices in any other state. Stevens argued that the 21st Amendment gave states broad powers to regulate liquor and that the court should at least demand proof of interference by the law on interstate commerce before "gutt[ing] the constitutional provision." Justice William J. Brennan Jr. took no part in the case.

In another case yesterday, a narrowly divided court expanded a major Warren Court ruling, deciding that an accomplice's confession can never be used in court unless the accomplice can be cross-examined.

Brennan, writing for the five-member majority, said the Sixth Amendment, which guarantees a defendant's right to confront witnesses against him, does not allow an accomplice's confession to go unchallenged because such statements are inherently "suspect and must be subjected to the scrutiny of cross-examination."

Brennan, citing his opinion in a 1968 case, Bruton v. U.S., said a codefendant in a case has a "strong motivation to implicate the defendant and exonerate himself." Several opinions in recent years tended to limit the practical impact of Bruton, but yesterday's ruling in Lee v. Illinois reinforced it.

The case involved a double murder committed in East St. Louis in 1982 by Millie R. Lee and her boyfriend, Edwin Thomas. Both admitted taking part in the killings, but Thomas told police that the murders were premeditated. His statements were allowed in court even though he was not available to be cross-examined.

Brennan said "the right to confront and cross-examine adverse witnesses contributes to the establishment of a system of criminal justice in which the perception as well as the reality of fairness prevails."

Brennan sent the case back to the Illinois courts to determine whether Thomas' statements significantly affected the outcome of the trial.

Justice Harry A. Blackmun sharply dissented, accusing the majority of being "overly concerned with theory and pronounced principles for their own sake, and disregard[ing] the significant realities that so often characterize a criminal case."

Blackmun, joined by Chief Justice Warren E. Burger and Justices Lewis F. Powell Jr. and William H. Rehnquist, said, "There is a real world as well as a practical one. This case, centering on two senseless and reprehensible. . . murders, is illustrative."

Blackmun said the "majority points out correctly that the court customarily has treated confessions of codefendants with suspicion. Never, however, has the court held such confessions [always] inadmissible. . . . "