Federal authorities, capping a three-year investigation, are preparing insider-trading charges that could ensnare consultants, investment bankers, hedge-fund and mutual-fund traders, and analysts across the nation, according to people familiar with the matter.

The criminal and civil probes, which authorities say could eclipse the impact on the financial industry of any previous such investigation, are examining whether multiple insider-trading rings reaped illegal profits totaling tens of millions of dollars, the people say....