Only one kind of conservative has cause to cheer William Rehnquist's selection to be chief justice: the inconsistent kind. Rehnquist believes that taking life is constitutional when capital punishment is the issue. When it's abortion, he thinks the Constitution favors protecting life. Let children be born, but electrocute, gas or inject them if they end up on death row.

Rehnquist appears to have greater fervor for death than life. In April 1981, when only four prisoners had been executed despite the Supreme Court's having reinstated the death penalty five years before, Rehnquist attacked his colleagues for slowing the pace of killings through ''arcane niceties'' and ''procedural protections.'' The court was making a ''mockery of our criminal justice system.'' Cons were meeting more with their lawyers than their Maker. There ''can be little doubt,'' Rehnquist wrote, ''that delay in the enforcement of capital punishment frustrates the purpose of retribution.''

If what has happened since that outburst means anything, Rehnquist, the kill-'em-quicker judge, must be overcome with the joys of self-satisfaction: 55 people have been executed in state prisons since 1981.

In protecting life before birth, Rehnquist has not been similarly outspoken. In the 1973 Roe v. Wade abortion case, in which the court ruled that ''the unborn have never been recognized in the law as persons,'' Rehnquist was one of two dissenters. Less forceful than Justice Byron White, who called the decision ''an exercise in raw judicial power,'' Rehnquist saw the court creating ''a right that was apparently unknown to the drafters of the amendments.''

Among the red-hots of the right, Rehnquist is a leader for his views. Ronald Reagan shares them. The difference between the two is that Rehnquist is said to have, in the words of Benno Schmidt Jr., ''extraordinary intellectual power,'' while no one, at least with a straight face, has said that about Reagan. If Rehnquist's intellect is extraordinary, why is such a fundamental idea as the sacredness of life ignored? Where is the scholarship in declaring that convicts aren't being killed fast enough? Why not a similar zeal for improving the conditions in state prison systems, three-fourths of which have been declared unconstitutional?

Rehnquist's positions on capital punishment and abortion do little to help the right wing get beyond its reputation for caring about fetuses more than people. The justice, admittedly, is less rabid than others in the flock. Phyllis Schlafly, a Rehnquist admirer, opposes abortions but not incinerations: ''the atomic bomb is a marvelous gift that was given to us by a wise God.''

The chief justice-designate has issued no statements on God's military generosity. About his own gifts to the people, such as the 1981 call for more executions, Rehnquist has spoken: ''I came on the court, the boat was kind of keeling over in one direction. I felt that my job was . . . to kind of lean the other way.''

Are Supreme Court judges paid to lean or stand tall? Are they appointed to interpret the public drift or the Constitution? Rehnquist's statement was political, not judicial. The keeling he claims to have sighted on the open seas of American politics was presumably to the left, which was sufficient mandate to do the people's business by leaning right. The barque of justice would be straightened. Sail on, America.

By his positions on capital punishment and abortion, Rehnquist was using his interpretation of the Constitution to say who lives and who dies. Some should, some shouldn't. Is it conceivable that the Constitution itself is both life-affirming and death-dealing?

Rehnquist's inconsistency might be more noticed if he were in less a herdish throng of like-minded conservatives. His position is tolerated, even respected, by many on the left because they go both ways themselves, except in reverse. They oppose the death penalty but support the taking of life before birth. On the Supreme Court, William Brennan and Thurgood Marshall have taken those positions.

People who favor life in all circumstances -- for the fetus, the death-row prisoner, the conscripted soldier, the lab animal, endangered plants and trees -- find themselves on the margin of American politics. The term "pro-life" has been taken over by advocates for the unborn. But for the advocacy to mean more than sloganeering, all life needs to be revered. Few in public life -- from Congress to the courts -- are willing to risk it.