WASHINGTON - Sixteen years have passed since the Supreme Court's controversial decision in Roe v. Wade. It struck down the abortion laws of 40 states and wrote into the Constitution a brand-new interpretation of a pregnant woman's "liberty." Now the bells are tolling.

Attorney General Richard Thornburgh predicted on Sunday that the decision will be overruled. President Bush has called for an end to a right of abortion.The means toward that end are at hand. Earlier this month, the court agreed to hear argument in William L. Webster v. Reproductive Health Services.

Webster is attorney general of Missouri. He is defending a state law that lays certain requirements on physicians before they may perform an abortion; the act prohibits the use of state funds for "encouraging or counseling a woman to have an abortion not necessary to save her life," and it inhibits abortions in other ways.

Under the act, which was to have become effective in 1986, a physician must explain the risks of abortion to his patient. Another section requires that after the first 16 weeks, all abortions must be performed in hospitals rather than in outpatient clinics. The record contains testimony that a hospital abortion costs $2,500, an outpatient abortion between $350 and $650.

Before the law could become operative, a group of physicians and nurses sued for summary judgment declaring it unconstitutional under the rule of Roe v. Wade.

A U.S. District Court agreed: The law amounted to an impermissible intrusion into the privacy of the doctor-patient relationship. It trampled upon rights of free speech. The 8th Circuit Court of Appeals affirmed, and the state appealed.

The U.S. solicitor general, siding with Missouri, has filed a brief saying that if the high court is prepared to reconsider Roe, "this case presents an appropriate opportunity to do so."

In its essentials, the Missouri law scarcely can be distinguished from a similar statute in Pennsylvania - a statute the court nullified three years ago.

But since the Pennsylvania case was decided, the composition of the court has changed. What was unconstitutional in June of 1986 may not be unconstitutional in June of 1989.

As court observers many times have remarked, more in honesty than in cynicism, ours is in fact a government of men, not laws. Roe was decided by a vote of 7-2, with Justices Rehnquist and White dissenting from the opinion written by Justice Blackmun. Of the seven who formed the majority in 1973, only three remain.

Since then, the seats occupied by Burger, Douglas, Stewart, and Powell have gone to Justices Stevens, O'Connor, Scalia and Kennedy. The Constitution hasn't changed, but the judges have changed.

White and Rehnquist have vehemently opposed Roe from the very beginning. White termed the court's 1973 decision "an exercise in raw judicial power." Rehnquist consistently has regarded Roe not as jurisprudence but as legislation.

It is a fair presumption that Rehnquist and White have not changed their minds. Justice O'Connor is regarded as a third vote to overrule. If newcomers Scalia and Kennedy should be persuaded that Roe was a terrible piece of constitutional law, which it was, there goes Roe v. Wade, 5-4.

My guess is that in deciding the Missouri case, a majority will be mustered that will pay some measure of deference to the aging Justice Blackmun. Instead of junking Roe completely, a way will be found to preserve a respectable shell.

The states will be accorded power to discourage abortion and to erect formidable obstacles in its path, but at least in the earliest stages of pregnancy, abortion may not be prohibited altogether.

Surgeon General C. Everett Koop took a dismal view of the prospects. If Roe were overruled and control returned to the states, "it will open Pandora's box, because we'll have 50 problems instead of one."

To those of us who believe in federalism, that prospect is not appalling at all. The states are perfectly capable of responding to the wishes of their citizens. Their view of "liberty" is at least as informed as Justice Blackmun's.