WASHINGTON » Will your new car get an A in fuel efficiency? A government proposal might add letter grades to showroom window stickers on new cars and trucks to reflect a vehicle’s overall fuel economy and greenhouse gas emissions.

The Transportation Department and Environmental Protection Agency said yesterday they were considering two options to upgrade the energy and environmental information that will adorn labels on new vehicles in car dealership showrooms, beginning with the 2012 model year. The government is considering a letter grade approach or updating the design of the current sticker to include comparisons of a vehicle’s fuel economy and tailpipe emissions.

Consumers scan the window stickers to compare vehicles when shopping for a new car or truck. The stickers have not been updated significantly in three decades.

"From electric to plug-in hybrid vehicles, we think a new label is absolutely necessary to help consumers make the right decision for their wallet and for the environment," said Gina McCarthy, the EPA’s top air pollution official. The changes are required under a 2007 energy law.

The government wants the labels to reflect emerging vehicle technologies and account for greenhouse gas emissions affecting the environment, but they would not include pollution from power plants that recharge electric vehicles.

Under the letter grade proposal, an average vehicle on fuel efficiency and emissions would receive a B-. Electric vehicles would receive an A+, plug-in hybrid electric vehicles would earn an A and three gas-electric hybrids — the Ford Fusion Hybrid, Honda Civic Hybrid and Toyota Prius — would get an A-.

The best-selling passenger car in America, the Toyota Camry, would receive a B or a B-, depending on the vehicle’s engine. Hybrid versions of the Camry would earn a B+. The top-selling pickup truck, the Ford F-150, would receive a C+ or a C, based on the engine variant.

Luxury models such as the Ferrari 599 GTB Fiorana and the Mercedes-Benz Maybach 57 would get a D+, and the Ferrari 612 Scaglietti would receive the lowest grade of D under the plan.

Automakers questioned the proposed letter grades, saying it might affect sales. Gloria Bergquist, a spokeswoman for the Alliance of Automobile Manufacturers, said "the letter grade inadvertently suggests a value judgment, taking us back to school days where grades were powerful symbols of passing or failing." She said a broad range of vehicle technologies were needed to improve fuel efficiency.

McCarthy said the letter grade option was not meant to be a judgment on the vehicle, but a "metric that consumers can use" when car shopping. The letter grade would include an estimate of how much money a motorist would save in fuel costs over five years.

The second option would maintain the current label’s focus on a vehicle’s miles per gallon rating and annual fuel costs but update the design and add new comparison information on fuel efficiency and vehicle tailpipe emissions.

David Strickland, administrator of the National Highway Traffic Safety Administration, said there was "no preferred option," and the government hoped to hear from the public during a 60-day comment period. The public can e-mail comments on the plans to newlabels@epa.gov, and a final plan is expected in early 2011.

Environmental groups said they generally supported the plan, noting it would help consumers make meaningful comparisons among vehicles and choose vehicles that will help them save money at the gas pump.

"You shouldn’t need a Ph.D. to buy a car. These proposed new labels will make it much easier for consumers to comparison-shop," said Vickie Patton, the Environmental Defense Fund’s general counsel.

Environmentalists said the information on the stickers should reflect power-plant pollution information on electric vehicles. The proposal would only factor in greenhouse gas emissions from vehicle tailpipes.

"Consumers shopping for a clean car need to be able to compare a Prius with an electric vehicle. Not knowing how much coal-burning power plants emit to recharge the electric vehicle obscures the choice," said Dan Becker, director of the Safe Climate Campaign for the Center for Auto Safety.