Abortion opponents, backed by the Bush administration, urged the Supreme Court Wednesday to overturn its landmark 1973 ruling giving women the right to terminate their pregnancies. The showdown spilled into the streets, where more than two dozen demonstrators were arrested.

"The United States asks this court to reconsider and overrule its decision in Roe vs. Wade," said Harvard law professor Charles Fried, who was asked to return to administration service for this one case.Fried was one of three lawyers participating in an hourlong argument over disputed Missouri abortion regulations - a case that has become a focal point for the emotionally charged battle over a woman's right to end her pregnancy.

"We are not asking the court to unravel the fabric" of individual privacy rights, Fried told the justices. "We are asking the court to pull this one thread."

But St. Louis lawyer Frank Susman, representing those who successfully challenged the restrictive Missouri regulations in lower courts, responded, "When I pull a thread, my sleeve falls off. There is no stopping. It is not a thread he's after."

Susman urged the justices to uphold the 1973 ruling, stating, "Women do not make these decisions lightly. They agonize over them. State legislatures have no business invading this decision."

Missouri Attorney General William Webster, defending the state's abortion regulations, said, "The government certainly is not obligated to become an advocate for abortion."

He contended that lower courts were "clearly wrong" when they struck down a state legislative declaration that "life begins at conception."

As the justices, with questions from the bench, probed the positions of each lawyer, the usually tranquil scene outside the court building offered an indication of how deeply public opinion runs on the issue.

Hundreds of demonstrators, "pro-life" and "pro-choice," carried competing banners and placards that said, "Keep Abortion Legal," "Women Must Have the Right to Choose" and "Abortion is Murder." There were 27 arrests on charges of unlawful entry for crossing police lines.

Missouri officials and the Bush administration are urging that Wednesday's case be used to overturn or curtail the court's landmark 1973 decision that women have a constitutional right to abortion.

Even if the court rules on the Missouri regulations narrowly, the decision will be viewed as a barometer of the justices' commitment to the 16-year-old ruling in Roe vs. Wade.

Justices appointed under President Reagan have strengthened the court's conservative wing, which is skeptical of the wisdom and continued vitality of the landmark decision.

The justices will take their initial vote in the Missouri case Friday, discussing their views and beginning the process of drafting and redrafting opinions to accompany the announcement of the court's decision, expected by July.

In an attempt to sway the justices, Americans in record numbers have been writing and telephoning the court. Tens of thousands of letters arrive each day, and the court's two switchboards were so flooded with calls that a rarely used third board had to be activated.

The 1986 Missouri law includes a variety of provisions that range from declaring that life begins at conception and that "unborn children have protectable interests in life, health and well-being," to provisions banning the use of state funds, employees or facilities for abortions.

The law also requires that doctors, prior to performing an abortion on any woman who a doctor has reason to believe is 20 or more weeks pregnant, perform tests to determine the viability of the fetus.

The federal government and a number of states have bans on the use of public funds for abortion, and the Supreme Court, in rulings in 1977 and 1980, generally upheld the bans. However, the Missouri law takes those rulings a step further, barring the use of state facilities even if the woman is willing to pay for the services.

Doctors, nurses and two non-profit corporations challenged the constitutionality of the law; the district court struck down the provisions, and the appeals court concurred.

The 8th U.S. Circuit Court of Appeals in St. Louis held the provisions of the law were unconstutional and designed to erect obstacles "in the path of women seeking full and uncensored medical advice about alternatives to childbirth."