WASHINGTON – Top Trump administration officials are engaged in a heated debate over how to undo federal fuel-efficiency targets for cars and light trucks, as manufacturers voice concern that a major rollback of an Obama-era rule could go too far and fracture the nation’s auto market. The internal negotiations over relaxing carbon-emission limits for cars and SUVs slated to be sold in model years 2022-2025 underscore the challenge officials face in trying to fulfill President Donald Trump’s 2017 promise to ease the regulatory burden on Detroit. Some of the same companies that had pressed for action now worry that they will be forced to comply with two standards: the stricter specifications that California imposes on its massive auto market and a separate requirement for the rest of the country. Within the next few days, several administration officials say, the Environmental Protection Agency will announce that it has concluded automakers cannot meet the fuel-efficiency guidelines set by the previous administration.