The state’s highest court today said it has opened a formal inquiry into whether the state’s acquittal rate at drunk driving trials presided over by district court judges – a rate that eclipses 80 percent – is inordinately excessive, a step it said is necessary assure “the integrity of the judicial process.’’ The Supreme Judicial Court’s announcement comes a day after the Globe Spotlight Team reported Sunday that the judges’ acquittal rate is about 30 percentage points higher than the acquittal rate by juries – a degree of leniency that specialists have said is virtually unsurpassed in the United States.