THE QUESTION arises out of two contradictory decisions handed down by the Supreme Court last week: Is the court living in this century on this planet with the rest of us? The answer seems to depend on what day of the week you ask.

Last Monday, the court handed down a decision in a Missouri case about the right to die. It tied the hands of family members in a manner indicating it had tuned out on modern-day medical technology. The other decision, issued two days later and involving the use of one-way television testimony in child-abuse cases, said yes, we accept scientific advancements, we put them to work.

A majority of the court sentenced Nancy Cruzan to life last Monday. She is 32 and has been in an irreversible coma for seven years. She lives because a tube has been planted in her stomach so she can be fed. Her family wishes to remove the tube. The State of Missouri said no. The court upheld Missouri.

She could live another 30 years in this condition. Why? Well, writing for the majority, Chief Justice William Rehnquist says the state has an interest in keeping her alive.

Obviously, the framers of the Constitution did not foresee technological advances of the sort that keep Nancy Cruzan "alive." The court insisted that there was no "clear and convincing" evidence that Nancy Cruzan would have wanted the solution that her parents are seeking,

There was, however, evidence. Actually, although she was only 25 at the time of the car smashup that ended her life as a normal human being, she had thought about the plight she ended up in. She told a housemate that she never wanted to live as "a vegetable." She told her sister the same. They remember the melancholy circumstances which prompted these reflections: Nancy Cruzan's grandmother died. She thought death was preferable to the limited existence that was the alternative. A baby in the family was stillborn. The child's prospects had been miminal; Nancy Cruzan thought death was a deliverance.

But that was not good enough for Rehnquist and his four concurring justices. Nancy Cruzan did not specifically cite a "desire to have hydration and nutrition withdrawn." In that case, the majority ruled, the state superseded the family in judging the intention, if not the interests, of the incompetent patient.

In dissent, Justice William F. Brennan Jr. addressed the human consequences of such sticklerism. He expressed movingly the almost universal longing about the end of life: "A quiet, proud death, bodily integrity intact, is a matter of extreme consequence."

"The timing of death," he observed, "once a matter of fate -- is now a matter of human choice. " At the time the framers were drafting, people died when their time came, not when a plug was pulled.

In a separate dissenting opinion, Justice John Paul Stevens wrote, "An innocent person's constitutional right to be free from unwanted medical treatment is thereby categorically limited to those patients who had the foresight to make an unambiguous statement of their wishes while competent."

He is right, of course. We must all hasten to our lawyers and fill out a living will, so that the authorities do not have the power to keep us breathing beyond our power to enjoy life.

The idea that the enlightened men who wrote the Constitution would want to prolong death is not compelling. They were supremely rational men and they believed in "the pursuit of happiness." They could not foresee monstrous technological marvels which foil nature.

Is that what Rehnquist would want for himself or a member of his family? In another decision filed two days later, the court made friends with the 20th century, acknowledging that technological developments have made it possible to loosen constitutional stays for good reason. In this case, the good reason was the protection of children-witnesses in child-abuse cases.

The practicality of letting a child tell the story on closed-circuit television takes precedence over the constitutional right of defendants to confront their accusers -- if the prosecution demonstrates that the "child witness would be traumatized" by having to testify before the accused tormentor.

Justice Sandra Day O'Connor's majority opinion added: "A state's interest in the physical and psychological well-being of child-abuse victims may be sufficiently important to outweigh, at least in some cases, a defendant's right to face his or her accusers in court."

She is right, of course. It is a sensible and humane decision.

She voted with Rehnquist on the Cruzan decision. She wrote a separate opinion in which she gave the matter its only redeeming social value. She suggested it was time for the states to figure out who has the right to pull the plug.

Mary McGrory is a Washington Post columnist.