With the nominations of William Rehnquist as the next chief justice and Antonin Scalia as associate justice, there has been much talk of the role of ideology in Supreme Court appointments. Most of that discussion has correctly assumed that the president has the right -- or even the duty -- to nominate judges on the basis of ideological compatibility.

What is disturbing, however, is the implicit or explicit rejection of the corollary proposition: that the Senate should also consider ideology in its confirmation process. Sen. Orrin Hatch, for example, said that it "would be a disgrace to fight Rehnquist and Scalia on ideological purposes." Unnamed Democrats also conceded (according to a report in The Post) "the president's prerogatives to select whomever he wished," subject only to a "fair but thorough confirmation process."

*Thus those who will act on the nominations seem to believe that it is the president's job to select Supreme Court justices on the basis of ideology and the Senate's job to screen the nominees only on the basis of qualifications.

This one-sided view of the role of ideology in the appointment of Supreme Court justices is based on a misperception of the entire structure of the Constitution. To reject the Senate's ideological role in choosing Supreme Court justices is to set at naught the Framers' ingenious system of checks and balances.

Wholly trusting neither the executive nor the legislature, the Framers carefully constructed a Constitution that requires the joint action of both to achieve any significant governmental action. No laws may be enacted, no treaties implemented, no judges appointed, without the concurrence of members of both branches.

Even slight deviations from this scheme are not tolerated. Illustrations of the primacy of legislative and executive interdependence in our constitutional scheme include the court's recent invalidation of the legislative veto device (with Justice Rehnquist dissenting on unrelated grounds), and the court's expected invalidation of portions of the Gramm-Rudman Act.

It is ironic that a judge who played a major role in invalidating Gramm-Rudman and a justice who consistently purports to be guided solely by the intent of the Framers are the central focus of a philosophy that so ignores these principles.

Both history and precedent mandate the maintenance of the constitutional balance of power: the Senate, no less than the president, should consider ideology in deciding whether to confirm the two nominees.

There is a standard response to any argument that the Senate, too, must consider the nominee's ideological fitness for office. It is to suggest, with appropriate historical illustrations (the favorites are Chief Justice Earl Warren and Justices Hugo Black and William Brennan) that it is impossible to predict how a judge's philosophy will evolve once he or she has been on the bench for some time.

Once the constitutional guarantee of lifetime tenure removes the political and other pressures that might otherwise influence the nominee's political development, the new justice has the freedom to grow and change intellectually and politically, and thus the potential to surprise or disappoint the president ideologically. This evolutionary proces is thought to be a natural check on a president's ability to "stack" the court ideologically, obviating any need for the Senate to examine anything except the intellectual and legal qualifications of the nominee. Justice Rehnquist himself has espoused this view.

This is not a reliable check on the president's power, however, and a look at Rehnquist and Scalia offers a good example of why. With both of these nominees, there is little or no chance of the sort of unpredictable intellectual development cited, since both have been insulated from political pressures for many years. Rehnquist has been on the high court for over a decade; it is highly unlikely that elevation to chief justice will change his political philosophy in any significant respect. While Scalia has not been on the federal bench for as long, his lengthy tenure as a professor at various law schools has similarly enabled him to develop a political philosophy free from ordinary political constraints.

By contrast, Chief Justice Warren was governor of California at the time of his appointment to the court. Justice Black was a U.S. senator, and Justice Brennan was sitting on a state court. All three had thus been subject to considerably more political pressure than a life-tenured federal judge or a life-tenured law professor.

* Those who are encouraging the Senate to focus solely on qualifications of judicial nominees are suggesting that the president alone should have the power to shape the politics of the Supreme Court for years to come. Undermining the constitutional balance of power in this way would be dangerous enough in the context of treaties or ambassadors. In the context of the Supreme Court it would be disastrous, because the court, unlike treaties and ambassadors, has its own role in maintaining the constitutional balance: the practice of judicial review guarantees that without the concurrence of the Supreme Court, even the legislature and executive working together cannot prevail.

To allow one branch of this precisely balanced trio to have undue influence on another is to shake the very foundations of our republic.

The writer is an associate professor of law at the University of Minnesota.