MOSCOW — Russian President Vladimir Putin has ordered a major change in the rules for parliamentary elections, a move that could help solidify his power and influence toward the end of his current term and insulate him from dwindling public support for United Russia, the party that nominated him and currently holds a majority in Parliament.

At Putin’s direction, half of the 450 seats in the State ­Duma, the lower house of Parliament, would be filled using a proportional system based on votes for parties, with each party then filling its allotted seats.