WASHINGTON—A new energy agenda being fashioned by the Senate will do little to force automakers to substantially increase fuel economy, even though cars and SUVs consume 40 percent of the oil that is used daily in the United States.

The Senate rejected a requirement that automobiles cut gasoline use by 45 percent over the next dozen years. Instead it approved an industry-supported measure that includes new requirements that must be considered before the government can impose future fuel economy improvements.

Opponents to the tougher automobile fuel measure argued that manufacturers would be forced to stop making larger cars and sport utility vehicles (SUVs), resulting in thousands of autoworkers losing their jobs and forcing consumers to buy smaller, less safe vehicles.

Sen. Richard Durbin, D-IL, called such claims a red herring and said his amendment, demanding that new cars achieve a fleet average of 40 mpg by 2015, was technologically feasible without making vehicles smaller or resulting in industry job losses.

The average fuel economy for passenger vehicles has been declining since 1988, as more motorists have favored buying vehicles that are not required to meet as stringent fuel economy standards.