A unanimous Supreme Court ruled yesterday that if a person is accused of committing a crime purposely, the jury can't be instructed that the law presumes him to have intended to have achieved "the ordinary consequences of his voluntary acts."

Such an instruction violates the constitutional guarantee that the state must prove every element of a criminal offense beyond a reasonable doubt, Justice Willaim J. Brennan Jr. wrote in the opinion for the court.

The case involved the 1976 murder and sexual assult of Annie Jessen, 89, of Anaconda, Mont. She had been hit on the head with a shovel and stabbed in the back. The sexual assault occurred after death. Three weeks later, David Sandstrom, 18, who had been arrested in a burglary, confessed and was charged with "purposely or knowingly" causeing Jessen's death.

At trial, defense counsel said that Sandstrom admitted killing the woman but did not do so purposely or knowingly. Citing the testimony of two court-appointed mental health experts, the lawyer said that Sandstrom had acted out of a personality disorder aggravated by heave drinking.

Consequently, the lawyer said Sandstrom was innocent of "deliberate homicide" but could be charged with a lesser crime.

The disputed jury instruction followed with the trial judge saying to a protesting defense counsel's arguments, "you can give those to the Supreme Court."

The jury convicted Sandstrom of deliberate homicide.He drew a 100-year sentence. The Montana Supreme Court upheld it, only to be reversed yesterday.

The court took other actions.

INDIAN CHILDREN

Between 1969 and 1974, 25 percent to 35 percent of all Indian Children have been separated from their natural parents, usually to be placed with non-Indians. The basic reason: courts or agencies have ruled that the children will get a better upbringing away from Indian communities.

One such child is Tiffany Butts, now 10, daughter of Bernadine R. Brokenleg, a full-blooded Sioux, and Bernard C. Butts Jr. The child's physical features are those of a non-Indian.

She was 18 months old when her parents' marriage was annulled. She was cared for much of the time after that by her paternal grandparents in Kermit, Tex.

Texas state courts granted their petition to adopt her, Rejecting her mother's plea to take Tiffany to live with her on the Rosebud Indian Reservation in South Dakota.

The case was one of the key factors in moving Congress late last year to enact legislation ending the jurisdiction of state courts in parental rights cases involving Indian children such as Tiffany.

Yesterday, without comment, the Supreme Court delined Brokenleg's petition for review of the Texas state courts' decision.

In a friend-of-the-court brief urging review, the American Academy of Child Psychiatry said that the Tiffany Butts case "has grave implications for American Indian children."

LUGGAGE SEARCH

A unanimous court struck down a Puerto Rican law that gave police broad power to search the luggage of travlers from the mainland United States.

The justices ruled that the Constitution's protection against unreasonable police searches applies to Puerto Rico and that luggage searches conducted without "probable cause" to suspect a crime are unconstitutional. The Puerto Rican Supreme Court had upheld the law.

The decision struck down the marijuana possession conviction of Terry torres, who in 1977 was sentenced to one to three years in prison.

Torres was arrested after arriving from Miami at Puerto Rico's Isla Verde Airport on Aug. 7, 1976. Police said they search his luggage because Torres appeared nervous. They found one ounce of marijuana and a pipe with marijuana residue in addition to $250,000 in cash.

Torres challenged the 1975 law that gave Puerto Rican police such broad search powers, arguing that it violated the Constitution's Fourth Amendment.

NARCOTICS

The court left intact a Louisiana law making life in prison the mandatory penalty for distributing heroin.

The justices refused to hear arguments that the state law is unconstitutional because it imposes "cruel and unusual" punishment.