If the Obama administration persuades the Supreme Court to uphold its health care overhaul law, it will be in large part thanks to a 70-year-old precedent involving an Ohio farmer named Roscoe C. Filburn.

 

Mr. Filburn sued to overturn a 1938 federal law that told him how much wheat he could grow on his family farm and made him pay a penalty for every extra bushel.

 

The 1942 decision against him, Wickard v. Filburn, is the basis for the Supreme Court’s modern understanding of the scope of federal power. It is the contested ground on which the health care case has been fought in the lower courts and in the parties’ briefs. And it is likely to be crucial to the votes of Justices Anthony M. Kennedy and Antonin Scalia, who are widely seen as open to persuasion by either side.