The Supreme Court yesterday reversed a conviction based on statements obtained by a detective from a seriously and painfully wounded man while he lay at the edge of consciousness with an oxygen tube in his throat, a tube from his nose to his stomach to prevent vomiting, and a cathether in his bladder.

What the suspect told the officer was not "the product of his free and rational choice," Justice Potter Stewart wrote in the opinion for the 8-to-1 court decision. "To the contrary, the undisputed evidence makes clear" that Rufus J. Mincey "wanted not to answer" the detective who questioned him almost continually for four hours in a hospital intensive-care unit in Tucson, Stewart said.

"But Mincey was weakened by pain and shock, isolated from his family, friends and legal counsel, and his will was simply overborne," Stewart continued. "Due process of law requires that statements obtained as these were cannot be used in any way against a defendant at his trial."

The only dissent came from Justice William H. Rehnquist. The court "goes too far in substituting its own judgement" for that of the trial court and the Arizona Supreme Court, he wrote.

But he joined in a 9-to-0 ruling in another part of the case that officers violated the Fourth Amendment when they made a four-day warrantless search of Mincey's apartment, opening drawers, closets and cupboards and inspecting the contents; emptying clothing pockets; ripping up carpets and seizing 200 to 300 objects.

The case began in 1974 when Mincey, a 23-year-old Air Force machinist, allegedly agreed to sell heroin to Barry Headricks, an undercover police officer. Claiming he had to get money, Headricks left the apartment. He returned with nine plain-clothesmen and a deputy county attorney.

Acting as if alone, Headricks was readmitted to the apartment by one of Mincey's acquaintances in the living room. The other officers then forced their way in. Shots were fired in the bedroom. Headricks staggered out, fatally wounded. Mincey, wounded and semiconscious, was on the bedroom floor. Shortly, homicide officers arrived to start the four-day warrantless search.

Suffering "unbearable" pain, evidently confused, and depressed nearly to the point of coma, Mincey arrived at the hospital. There, the detective ignored his repeated pleas to be left alone, at least until he had a lawyer.

Mincey was convicted of murder, assault and three narcotics offenses. On state law grounds, the Arizona Supreme Court reversed the murder and assault convictions.

It upheld the narcotics convictions, ruling that a "murder scene" creates an exception to the requirement for a search warrant, and that the trial court ws not clearly and manifestly wrong in ruling that for purposes of impeaching Mincey's credibility at trial, his statements to the detectives had been made voluntarily and therefore were admissible.