DETROIT – The Chevrolet Cruze, the most popular car in the U.S. last month, will come in a diesel version that could boost gas mileage to around 50 mpg, two people briefed on General Motors Co. product plans said Monday.

A diesel Cruze would help GM meet more stringent government gas mileage requirements. It also would rival the efficiency of the popular Toyota Prius gas-electric hybrid, which gets 51 mpg in the city and 48 on the highway, according to estimates from the Environmental Protection Agency.

The diesel Cruze won’t hit showrooms until at least 2013, according to one of the people, both of whom asked not to be identified because the company hasn’t made a formal announcement.

The people didn’t know the price of the Cruze. Cars with diesel engines generally cost more than those with gasoline engines because they are more expensive to produce.

The base version of the Cruze now starts at $16,525.

The diesel Cruze would be built at GM’s factory in Lordstown, Ohio, southeast of Cleveland.

GM spokesman Tom Wilkinson would not comment on the diesel engine.

GM, which has an Allen County truck assembly plant, sold about 25,000 Cruzes last month, vaulting the model past perennial leaders such as the Toyota Camry and Honda Accord to become the best-selling car in the U.S. Both Toyota and Honda had fewer models to sell because of parts shortages caused by the March 11 earthquake and tsunami in Japan.

GM has several diesel-powered cars in other parts of the world, including a 2.0-liter, four-cylinder turbocharged diesel Cruze that’s selling well in Australia.