The United States imposed 25 percent tariffs on imported auto parts on Saturday that could sharply raise prices for new and used vehicles as well as for repairs and insurance. The latest tariffs, which President Trump ordered in March as part of his plan to promote domestic manufacturing, come after the 25 percent levies on imported cars that took effect in early April. This second round of duties on imported parts will have a broader impact because even cars made in the United States often have engines, transmissions, batteries or other components produced in other countries. The administration said on Tuesday that the tariffs were intended “to protect national security by incentivizing domestic automobile production and reducing American reliance on imports of foreign automobiles and their parts.”