CLARENCE THOMAS'S nomination to the Supreme Court has generated controversy in part because he endorses a natural-law philosophy. The debate over the proper role of natural-law thinking in the interpretation of our Constitution does not break down on ideological grounds; it is not an argument between liberals and conservatives. Though this debate dates back to the Framers, it is as current as the controversy over Robert Bork's failed nomination.

No issue divided Judge Bork and me as much as this single question: Are there fundamental rights -- not explicit in the Constitution -- that are protected by that document? My answer to that question, relying on principles of natural law, was an emphatic "yes" -- a view that Judge Thomas, who has sharply criticized Judge Bork's original-intent jurisprudence, appears to share.

But to say that Clarence Thomas and I stand on the same side of the natural-law divide is not to say that his Supreme Court nomination is one I can certainly support. For there are a wide range of philosophies that fit under the rubric of "natural law" or "natural justice."

Some "natural law" adherents belong to a "higher law" school, teaching that God has established a code of "right" and "wrong." Others believe that a set of principles of "right moral conduct" can be rationally deduced. Still others conclude that "natural justice" encompasses certain rights that are inherent in all men. Which variety of natural-law thinking would Clarence Thomas bring to the Supreme Court?

The question is vital because natural-law arguments have been used to support conflicting conclusions: to attack the legitimacy of slavery -- but also to defend it; to demand equal rights for women -- but also to deny them. Still today, such reasoning is being used to defend a constitutional right to privacy -- but also to assault it.

To me, there are four basic questions concerning Judge Thomas's views on natural law that must be addressed by him in the coming confirmation hearings:

Would he place his belief in natural law above his oath to the Constitution, or would he instead restrict the use of natural law ideas to the task of giving meaning to the Constitution's great, yet sometimes ambiguous, phrases?

Does he view natural law's function as being a specific moral code regulating individual behavior, or does he instead believe that natural law protects individual freedom, even in areas of moral choice?

Does he see natural law as a static set of unchanging principles, or does he instead see it as an evolving body of ideals?

Would he use natural law to limit government's ability to respond to changing circumstances, or would he instead acknowledge that natural law must adjust to new social challenges? The first question -- whether Judge Thomas places natural law above the Constitution -- can be addressed succinctly. In our system, the sole obligation of a Supreme Court justice is to the Constitution. Natural justice can supply one of the important means of understanding the Constitution, but natural law can never be used to reach a decision contrary to a fair reading of the Constitution itself.

If Clarence Thomas believes that the Supreme Court should apply natural law above the Constitution, then in my view he should not serve on the Court.

Second, does Judge Thomas see natural law as a "moral code," or does he understand it to be a protector of personal freedom? We must never forget that the central natural-law commitment made by this country is the commitment to individual freedom. But not all versions of natural law share this commitment. For some, the highest use of natural-law reasoning is to state a code of behavior for all people to follow in their individual lives; a code that the government must enforce.

The implications of this "moral code" approach are extraordinarily wide-ranging. For example, women were once barred from becoming lawyers by the Supreme Court in a "natural law" case, Bradwell v. Illinois, in 1873. If this approach were imposed on the country today, it could lead to the banning of contraceptives, the regulation of our private sexual relations -- the prohibition of any conduct deemed "immoral."

Should our country adopt such a version of natural law, the only moral choices that would remain to individuals would be choices between alternatives that had no moral consequences, such as the choice between spending the evening bowling or listening to Beethoven, to use one example offered by Amherst College professor Hadley Arkes, an advocate of this natural law school.

As I argued during the Bork confirmation debate, the American tradition of natural law has been to protect the rights of individuals to make decisions about matters of moral significance -- free from both the interference of the will of the majority, as Robert Bork would have permitted, or from judges imposing their particular moral code, as some believe Clarence Thomas would have it.

While Judge Thomas has written passionately about limited government being the product of natural-law reasoning, and has said that natural law is "the best defense of liberty and limited government," there are other aspects of Thomas's views that are far less heartening.

Judge Thomas has said that "the thesis of natural law is that human nature provides the key to how men ought to live their lives" -- suggesting that natural law dictates morality to us, instead of leaving matters to individual choice. He has told us he believes that natural law provides the key to rekindling the kind of morality he favors.

One expression of Judge Thomas's views on a vital current issue -- reproductive freedom -- raises a profound question. Some natural law advocates believe not only that the right to choose recognized in Roe v. Wade should be discarded, but that the Constitution should recognize fetal rights and should be read to forbid all abortions in all 50 states and the District of Columbia.

In a speech in 1987, Judge Thomas praised an article adopting this extreme view, calling it a "splendid example of applying natural law" to the "meaning of the right to life."

Would Judge Thomas use natural law to impose a national moral code? This is a critical question for the hearings.

Next, is the nominee's vision of natural law a static one or an evolving one? For some, natural rights are wholly unchanging because they are "timeless truths." In this view, the meaning of the Constitution would be static, limited by the interpretations that would have been agreed to by the Framers -- or by some other natural law notion fixed even farther in the past.

Such a static conception of natural rights and of the meanings of our constitutional language is emphatically not the view held by such founders as Jefferson and Madison. They understood that constitutional guarantees would have to change and expand with time. Even in their own day, they saw the understanding of freedom of speech change and grow in response to the oppressive Alien and Sedition Acts.

Any such static reading of the Constitution misses the point of Chief Justice John Marshall's description of the Constitution as a document "intented to endure for ages to come," which would have to "adapt to the various crises of human affairs" in ways that "can be best provided for as they occur."

Natural law reasoning must be dynamic, capable of change. Only with expanding conceptions of "due process," "equal protection," and rights "reserved to the people" can the development of individual rights and liberties keep pace with the other changes in our country.

Although individual liberties in this nation have not always received their due respect, the prevailing tide of our history has run consistently toward liberty, and we have built the essential character of our nation at its high water marks -- the 13th, 14th and 15th Amendments guaranteeing fundamental individual rights; the 19th Amendment, guaranteeing women the right to vote; the right to equal educational opportunity in Brown v. Board of Education; and the decisions guaranteeing reproductive freedom. These and other profound changes have all been possible because of our evolving sense of natural justice.

Judge Thomas has argued that we must retrieve a sense of natural law that the founders had but that we have lost. Is such a call to "return to the founders" a harkening to a static understanding of natural law, or is there room in Judge Thomas's system for the growth and adaptation needed in our country?

An indication that he may reject the evolving view of natural law is his criticism of the Court's modern unenumerated rights decisions, including the Griswold decision protecting marital privacy. He was also a member of the Reagan administration working group that criticized the Supreme Court's expansion of privacy rights as "fatally flawed."

Moreover, Judge Thomas has complained of a modern "proliferation of rights" and has criticized Supreme Court opinions recognizing new personal freedoms. He has said that "the Supreme Court has used the due process and equal protection clauses in a variety of extremely creative ways," and one does not get the sense that this is meant to be a compliment. These are all signs of a static vision of natural law, a resistance to expanding Constitutional protections over time. Finally, would Judge Thomas employ natural law to limit government's ability to respond to changing circumstances, or does he see it as permitting the government to adjust to new social challenges?

For example, beginning in the late 1800s and extending into the 1930s, the Supreme Court interpreted the Constitution to invalidate legislation establishing maximum hours and minimum wages for workers, as well as portions of the New Deal legislation designed to produce economic recovery in the country. In these cases, the justices often invoked the language of natural law to prohibit effective government action.

Fortunately, the Supreme Court ultimately came to repudiate this version of natural law thinking, and recognized that the natural law "liberty of contract" need not stand in the way of legislative responses to changing economic conditions.

Nevertheless, there are some in the country today who look back with fondness on the Court's peculiar applications of natural law to defend a worker's "freedom to work" for unlimited hours, in unsafe conditions, or for less than the minimum wage.

It would be a grave mistake to invoke natural law to call into Constitutional doubt laws protecting us from environmental degradation, laws regulating the qualifications of child-care providers, and laws establishing minimum wages and workplace safety. This is decidedly not the direction in which the country should be moving.

Is this the direction that Judge Thomas's natural-law thinking would take us? Initially, I am heartened by the fact that Judge Thomas has chided conservative activists who seek a return to the most extreme aspects of the Court's 1920s jurisprudence in the fields of economic and property rights.

On the other hand, he has given signs that point in the opposite direction. He has scolded "government" for passing laws such as "licensing requirements" and "the minimum wage." And he has insisted that "economic rights are protected as much as any other rights" by the Constitution.

Do the "licensing requirements" that Clarence Thomas opposes include the government licensing of the operators of day-care facilities, or the people who work in pharmacies, or people who work in senior citizen centers? Does Judge Thomas's endorsement of the "right to own and control one's property" mean that the government cannot prevent someone from building a high-rise or a gas station next to your house? Does it mean that the legislature cannot prevent air or water pollution?

Others who advocate using natural law to establish the "new economic rights" and "property rights" have called these laws into question. Needless to say, if Judge Thomas adheres to this natural-law theory, and would roll back the clock to an earlier era's understanding of the Constitution, I would have grave doubts about this nomination.

His frequent use of the language of natural law makes it incumbent on him to be responsive to these and many other specific questions. The American people will be listening attentively to the nominee as he addresses these matters -- as will I.

Sen. Joseph Biden (D-Del.) is chairman of the Judiciary Committee.