JERUSALEM — Prime Minister Benjamin Netanyahu of Israel held a significant lead in his third electoral showdown with the former army chief Benny Gantz, and was on the cusp of an outright parliamentary majority, exit polls showed on Monday night.

If the polls are borne out by the official returns, Mr. Netanyahu, who faces trial in two weeks on felony corruption charges, could have the first chance to assemble a majority coalition and win a record fifth term in office.