EVERY FOUR YEARS, partisans at both ends of the political spectrum wring their hands at the devastation the other side will wreak if its presidential candidate gets to nominate the next four years' worth of federal judges. Conservatives warn that the courts will impose a liberal social agenda. Liberals fret about a "rollback" of basic rights. Somehow, the stakes always prove a bit lower than threatened. The courts generally seem to find a way to avoid diving off a cliff.

Still, the coming presidential election matters greatly for the courts. The next president is likely to have the chance to name a number of Supreme Court justices, influencing the direction of the high court for decades to come. Two justices -- one of the most conservative, Chief Justice William H. Rehnquist, and the most liberal, Justice John Paul Stevens -- are in their eighties; eight of the nine are 65 or older. On the charged issue of abortion rights, we think the court is unlikely to overturn Roe v. Wade, even if Mr. Bush gets to appoint several new justices. But no predictions are fail-safe, and new appointments likely would affect the court's approach to separation of church and state; the power of the federal government in relation to the states on civil rights and environmental regulation; and the right to privacy, including the reach of constitutional protection for gay rights.

In assessing what a second Bush term would augur for the courts, it makes sense to look at the first. Some of President Bush's nominees have been highly objectionable, and Mr. Bush, rather than working with Democrats to de-escalate the judicial nominations wars, too often has added fuel to the fire. But the demonization of his judges has greatly overstated their radicalism. They have been, on the whole, mainstream conservatives, for better and worse. Better, because such conservatism can imply a judicial restraint and a respect for the prerogatives of elected legislators; worse, because it can bring with it too cramped an understanding of rights we believe are guaranteed by the Constitution.

Sen. John F. Kerry made clear in the third debate that he would subject potential nominees to a litmus test on abortion, which we think is the wrong way to pick judges. Beyond that it's harder to predict the kind of judges Mr. Kerry would nominate, since he has no record. Few likely Democratic judicial nominees aspire to the aggressive judicial liberalism of the 1960s and 1970s -- even if such a nominee could win confirmation. Kerry nominees could be expected, in general, to display a greater solicitude for privacy rights, for federal power in the environmental and civil rights arenas, and for the rights of those whom the government would lock up or kill. Greater concern for these values comes at the cost of a more freewheeling jurisprudence, one less respectful of traditional state powers, less constrained by the text and history of the Constitution, and more willing to assert judicial power in areas where it has not traditionally operated.

This is a trade-off in which not everything we believe is on one side of the electoral equation. On balance, however, it favors Mr. Kerry, particularly now. The great protection against ideological extremism on the courts is ideological diversity, and it is far easier to imagine the Supreme Court's becoming preponderantly conservative in a second Bush administration than to imagine its becoming overbearingly liberal in the first four years of a Kerry administration. The possibility of conservative judicial radicalism, however overstated by liberal interest groups, certainly is greater today than the possibility of out-of-control liberal activism.

This is one in a series of editorials comparing the records and programs of the presidential candidates on important issues. Others can be found at www.washingtonpost.com/opinion/thechoice.