WASHINGTON — The Justice Department has spent three years over two presidential administrations building the case that Google illegally abused its power over online search to throttle competition. To defend itself, Google has enlisted hundreds of employees and three powerful law firms and spent millions of dollars on legal fees and lobbyists.

       On Tuesday, a judge in U.S. District Court for the District of Columbia will begin considering their arguments at a trial that cuts to the heart of a long-simmering question: Did today’s tech giants become dominant by breaking the law?

       The case — U.S. et al v. Google — is the federal government’s first monopoly trial of the modern internet era, as a generation of tech companies has come to wield immense influence over commerce, information, public discourse, entertainment and labor. The trial moves the antitrust battle against those companies to a new phase, shifting from challenging their mergers and acquisitions to more deeply examining the businesses that thrust them into power.