Not only did the justices open their session by declaring, in a separate case argued three months ago, that Congress lacked authority to make the federal law against age discrimination binding on the states. But then, during arguments on the constitutionality of the Violence Against Women Act, members of the same five-justice majority in the age discrimination case made abundantly clear their deep skepticism about whether Congress had an adequate basis for opening federal courts to suits by victims of violence "motivated by gender" against their attackers.

Congress passed the Violence Against Women Act in 1994, just before the Supreme Court set itself on its current course of subjecting to searching scrutiny any Congressional action that could conceivably impinge on state sovereignty or traditional prerogatives. In a sense, the statute and the court's growing list of federalism rulings have been on an inevitable collision course that ended in the courtroom this morning, with little evidence that the 5-to-4 states' rights majority would shift course.

"Your approach would justify a federal remedy for alimony, child support, even contract disputes," Justice Sandra Day O'Connor said disapprovingly to Solicitor General Seth P. Waxman, who was arguing the government's appeal of a ruling that the law's civil damages provision was unconstitutional.

Some students of the court have speculated that Justice O'Connor's record of solicitude for women's interests might, in this case, trump her demonstrated commitment to keeping federal power within distinct boundaries. But she gave little sign that she saw this case as in any way different from the other federalism cases, including the age discrimination case in which she announced the court's majority opinion today.

The Violence Against Women Act case is an appeal by a former Virginia college student, and by the Clinton administration on her behalf, from a ruling last year by the federal appeals court in Richmond that barred her from using the law to sue two fellow students, football players who she said had raped her in her dormitory room. The woman, Christy Brzonkala, sued after Virginia Tech took no action against one of the men and gave the other a deferred suspension that permitted him to keep playing varsity football.

The 1994 law has several other provisions, including a criminal section that provides for federal prosecution of interstate crimes of sex-motivated violence. The court last year refused to hear a constitutional challenge to the criminal provision.

The section at issue today in United States v. Morrison, No. 99-5, providing for private civil suits for damages, does not depend on whether a defendant has crossed state lines, because Congress wanted to provide a remedy for violence in or near homes. The absence of an interstate "hook," as Justice O'Connor described it, is a decided liability before a court that has taken a limited view of Congress's power to act under its authority to regulate interstate commerce.

Both Solicitor General Waxman and Julie Goldscheid, representing Ms. Brzonkala on behalf of the NOW Legal Defense and Education Fund, told the court that violence against women had a substantial impact on interstate commerce by deterring women from taking certain jobs or continuing their education.

In striking down the civil damages provision, the United States Court of Appeals for the Fourth Circuit said the law did not come within Congress's power to regulate interstate commerce because it did not address commercial activity. The court today appeared wary of adopting quite such a hard and fast rule, particularly after Michael E. Rosman, representing the defendants in Ms. Brzonkala's lawsuit, Antonio Morrison and James Crawford, said that in his view, Congress lacked constitutional authority to prohibit possession of narcotics for personal use because the activity was not commercial.

But even under a more elastic definition of activity that affects the economy, the justices appeared dubious about accepting the Congressional findings on the economic impact of violence against women.

If the justices find the Violence Against Women Act provision to be invalid under Congress's commerce authority, they could nonetheless uphold it under Congress's authority to enforce the equal protection guarantee of the 14th Amendment, a basis that the Fourth Circuit also rejected. Mr. Rosman, the defendants' lawyer, argued today that the 14th Amendment, which governs only official action, could not be a basis for a law that applies to private behavior.

The law's defenders argue that the statute is aimed at the failure of states to provide adequate remedies for violence against women, an aspect of official action, or inaction, that is appropriately the subject of legislation under the 14th Amendment. But Ms. Goldscheid's and Mr. Waxman's time at the podium ran out before they could address this aspect of their argument.

Mr. Rosman, general counsel of the Center for Individual Rights, a conservative public interest law firm, warned the court that if it upheld this law, "Congress could pass virtually any law" and "relegate the states to a trivial and unimportant role in our federal structure."

Justice Ruth Bader Ginsburg challenged that depiction. "What is the clash here?" she asked. She said Congress's goal was not to displace state authority but "just to provide an alternate remedy, an alternate forum."

She continued: "We are just complementing what the states do. Why can't Congress do that?"

"The power to regulate is the power to pre-empt," Mr. Rosman replied.

Justice Ginsburg persisted, noting that "we have so many parallels in discrimination legislation," with both the states and the federal government barring discrimination in employment and in public accommodations. Why can't the Violence Against Women Act coexist with parallel state laws, she asked.

"Because this is not commerce," Mr. Rosman replied. "This is violence, interpersonal violence, the kind of thing states have had as their exclusive province ever since the start of our country."

The Violence Against Women Act has generally been welcomed on the state level, with 36 states joining a brief in this case in support of the law. Only one, Alabama, filed a brief asking the court to declare the provision unconstitutional.