President Barack Obama's initiative to raise new tax revenue to pay for major policy changes likely will focus in the short run on tightening enforcement against businesses and wealthy individuals. In the long run, some experts believe it could lead to sweeping changes in the tax code itself.

White House officials disclosed the tax initiative on Tuesday, saying they intend to explore ways to better enforce the current code as well as improve it by eliminating corporate subsidies and untangling its many complexities. Mr. Obama...