WASHINGTON — A trade dispute over Canadian lumber that began when Ronald Reagan was president has become a political problem for President Biden, with home builders and members of Congress urging the administration to try to strike a deal that could help bring down the cost of critical building materials. But unlike other commodities that have been in short supply, lumber is also the subject of a long-running trade dispute between the United States and Canada. …But signs of diplomatic progress have been scarce, and Canadian lumber producers may soon face higher duties. …Finding a resolution to the trade dispute is unlikely to be a simple undertaking for the Biden administration. “There’s really nothing that the administration can do quickly,” said Scott Lincicome, a senior fellow at the libertarian Cato Institute, who criticized the lumber duties and the system that allows domestic industries to seek them.