Vice President Al Gore is pushing the Big Three American automakers for a firm commitment to begin producing vehicles in the near future that use fuel-efficient technology developed in a joint government-industry project, the Partnership for a New Generation of Vehicles. PNGV, launched in 1993 with the goal of producing a reasonably priced “supercar” by 2004 that gets 80 miles to the gallon, is expected to be expanded today to include light trucks. The aim of the new initiative will be to produce SUVs, minivans, and pickups that use a combination of electric and diesel engines to get up to 50 miles per gallon. But critics of the program say the Big Three have made little progress in getting greener cars to the market, despite government subsidies, even as Japanese automakers are producing much more fuel-efficient cars.