ONLY A FEW years ago, the Supreme Court appeared to be on the verge of gravely altering the balance of power between the federal government and the states. A string of opinions had restrained Congress's authority and bolstered state power in a fashion that, while appealing in certain areas, was badly off-base and dangerous in others. What made the court's newfound interest in what is called "federalism" scary was that nobody knew where it would stop. And if taken too far, the reinvigoration of state-level power threatened to encumber the federal government in such critical areas as civil rights and environmental protection.

But over the past year, the court has handed down a series of rulings that seem to indicate the limits of its enthusiasm for pumping up state authority. First, last year, it held that states are not immune under the 11th Amendment from suits for damages for violations of the Family and Medical Leave Act. This term, it followed up with a decision holding that states could be sued as well for damages for certain violations of the Americans With Disabilities Act -- though it had earlier immunized states against other violations of the same law. Then, last month, the court held in a 5 to 4 vote that a law barring lower federal courts from restraining "the assessment, levy or collection of any tax under State law" does not prevent federal suits challenging state laws that grant tax credits.

Cases in which the court declines to strike blows for states' rights often appear to be dogs that didn't bark, and they consequently tend to escape public notice. The tax credit case -- Hibbs v. Winn -- is a good example. As Justice Ruth Bader Ginsburg pointed out for the majority, federal courts for "a near half century . . . have entertained challenges to tax credits authorized by state law" without seeing the federal statute as getting in their way. So the decision did little more than validate a status quo that has long gone unquestioned. But a few years ago it would have been easy to imagine the justices deciding this case differently, that is, actively looking for ways to interpret the law to bolster state power.

It is still too early to say that the danger of an aggressive federalism jurisprudence has passed. The court has yet to define the limits of its recent interest in reining in Congress's historically broad power to regulate interstate commerce. Moreover, nearly all of the court's recent federalism cases have involved close votes, so changes in the court's composition could produce dramatic swings in doctrine. To a significant degree, in fact, the recent shift reflects the changing approach of a single justice: Sandra Day O'Connor. Still, the court's mood has clearly changed. No longer does the court appear to be reaching to remind Congress of the limits of its power and to generate maneuvering room for state governments under federal law. Now, rather, the court seems to be striving to put limits on its previous work.