The attorney general of New York, Eliot Spitzer, finally won one in court yesterday when he defeated an attempt by a group of banks, including JPMorgan Chase and Wells Fargo, to restrain him preemptively from subpoenaing their records. Mr. Spitzer prevailed on that procedural matter before Judge Sidney Stein of the federal court for the Southern District of New York. But as the attorney general goes on to attempt to regulate the practices of the national banks, he may have to make a detour through Congress.

Mr. Spitzer is attempting to obtain information from the banks about the mortgage rates they charge to minority homebuyers. Banks are required to collect and publicly release some of this information under the 1975 Home Mortgage Disclosure Act, enacted to prevent racial discrimination in the housing market. The publicly available data suggest to some people that the banks might be discriminating. Mr. Spitzer launched an investigation in April, and has requested that banks provide additional information.

The banks have argued that non-race factors, such as credit scores, explain the difference between mortgage rates for some minorities and whites that appeared in the public disclosure. Maybe. At issue, though, is which regulator should look into this – Mr. Spitzer or the U.S. Office of the Comptroller of the Currency, the federal agency charged with oversight of national banks.

Mr. Spitzer argues that states should be allowed to regulate the banks that do business within their borders. The banks argue that under federal law, the comptroller alone has authority to regulate national banks. A spokesman at the comptroller’s office, Kevin Mukri, says that the federal government has been scrutinizing claims of discriminatory lending for “many, many years.”

The National Bank Act of 1864 allows banks doing business across the country to obtain federal charters instead of having to grapple with banking laws in every state in the union. The law has created a two-track banking system. Large banks with operations in many states often choose to work with a single federal regulator. But state regulators are sometimes more open to innovative banking practices, making a state charter more attractive to some bankers.

The law has been the source of an ongoing turf war, in which Mr. Spitzer’s case is just the latest skirmish. Many state regulators have already tried to exert some authority over the banks, with little success. With lots of case law against him, Mr. Spitzer will have an uphill struggle in his attempt to apply New York’s antidiscrimination laws to national banks, yesterday’s procedural victory notwithstanding.

Which doesn’t necessarily mean that he shouldn’t be able to, and before this case is over, Congress may well have to revisit the issue, allowing the states to compete to offer regulations most likely to attract lenders. If nothing else, a debate on the National Bank Act would provide an opportunity to ensure that a Civil War-era law is still the best way to regulate American banks in the 21st century.

This debate, however, belongs, if it belongs at all, in Congress. Alexander Hamilton, an architect of the Constitution, went on to establish a federally chartered bank when he was treasury secretary. The place for Mr. Spitzer to pursue this one is in a Capitol Hill hearing room, not a federal courthouse. He might be on to something when he argues for a greater state role in banking regulation. Until then, though, our guess is that he’ll discover that the National Bank Act obtains even in New York.