WASHINGTON — Will your new car get an A in fuel efficiency? A government proposal may 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 Monday 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 and the government wants the labels to reflect emerging vehicle technologies and account for greenhouse gas emissions affecting the environment.

"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.

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."

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, (see above).

The public can e-mail comments on the plans to newlabels@epa.gov and a final plan is expected in early 2011.