The Supreme Court agreed yesterday to clarify a pivotal issue in libel suits by private individuals: whether the news media must prove a story is true or whether a person filing suit must prove it is false.

The case involves The Philadelphia Inquirer and a series the paper published 10 years ago about a beverage company's alleged ties to organized-crime figures.

The court has given the media substantial protections from libel suits by public figures such as politicians or entertainers. To collect damages, public figures must show that a story is false and that it was published with reckless disregard for the truth.

But the burden of proof is unclear when the plaintiff is a private person. In this case, Philadelphia Newspapers Inc. v. Hepps, the individual is the principal stockholder in the beverage company and is seeking compensation for financial losses as a result of a defamatory article.

Some states, including Maryland and the District, have ruled that the burden of proof in such cases lies with the plaintiffs and that they must show that an article was false. At least four others, like Pennsylvania, put the burden on the media and require that they prove that the story is true. About half of the states, including Virginia, appear to have no fixed rule on the issue.

The trial judge in this case, citing First Amendment protections for the media, ruled that the burden of proof was on the plaintiff. A jury decided in favor of the newspaper.

The state high court overturned that ruling and ordered a new trial. The justices will hear arguments in the case next winter.

In other action yesterday, the court voted, 5 to 3, to strike down as unconstitutional a New Mexico law that gave a $2,000 property tax exemption to Vietnam veterans, but only to those who lived in the state before May 8, 1976.

Chief Justice Warren E. Burger, writing for the majority, said the New Mexico law, like an Alaska law struck down in 1982, unconstitutionally "creates fixed, permanent distinctions between classes of concededly bona fide residents based on when they arrived in the state."

"Neither the Equal Protection Clause, nor this court's precedents," Burger said, "permit a state to prefer established resident veterans over newcomers" in apportioning certain benefits.

Justice John Paul Stevens, joined by Justices William H. Rehnquist and Sandra Day O'Connor, dissented in Hooper v. Bernalillo County Assessor.

The state's policy of giving special benefits to veterans was constitutional, Stevens argued, and the state was justified in limiting eligibility for financial reasons.

Justice Lewis F. Powell Jr. did not take part in the decision.

In another case decided yesterday, the court, adding to the power of military base commanders to keep out antiwar protesters, ruled that anyone previously thrown off a base can be prosecuted for reentering even during a base "open house." In a 6-to-3 ruling written by O'Connor, the court said that the First Amendment did not prevent the conviction and three-month prison sentence of James V. Albertini, who illegally entered Hickam Air Force Base in Honolulu.

Albertini was barred by formal letter from the base in 1972 after he poured blood on secret Air Force documents. He returned to the base in 1981 during a public open house and handed out leaflets protesting the nuclear arms race.

Albertini argued that the "open house" activities had made the base a public forum and gave him a constitutional right to be there despite the formal letter. A federal appeals court agreed, but the justices reversed.

"We are persuaded that exclusion of holders of bar letters during military open house will promote an important government interest in assuring the security of military installations," O'Connor said.

Stevens, joined by Justice William J. Brennan Jr. and Thurgood Marshall, dissented in U.S. v. Albertini. Stevens said Congress, in passing the law under which Albertini was convicted, "did not intend to punish" a visit during an open house.

The court, acting in a case pitting a stubborn young trial lawyer against the chief judge of the 8th U.S. Circuit Court of Appeals, ruled unanimously that the lawyer should not be suspended from practicing law for "a single incident of rudeness."

The lawyer, Robert Snyder of Bismarck, N.D., was fed up with the paper work required for court approval of reimbursement for attorneys who represent indigents in criminal cases.

When asked for more documentation in one case, he responded by writing that he was "extremely disgusted" by the treatment of lawyers who take such cases and said that he was "not sending you anything else. You can take it or leave it."

Chief Judge Donald Lay said the letter showed "disrespect" and demanded an apology. Snyder said "never." The court of appeals ordered him suspended for six months.

Burger, ducking the constitutional due process and free speech issues Snyder raised in In re Snyder, nevertheless overturned the suspension.

"Even assuming the letter exhibited an unlawyer-like rudeness, a single incident of rudeness or lack of professional courtesy," Burger said, "does not support a finding of contemptuous or contumacious conduct, or a finding that a lawyer is not presently fit to practice law in the federal courts." Justice Harry A. Blackmun did not vote.