Scituate officials are considering stricter fuel-efficiency guidelines for town-owned vehicles as part of the town’s participation in the state’s Green Communities Program. Standards currently require that all new vehicles have a fuel efficiency of at least 16 miles per gallon, said town planner Laura Harbottle. New guidelines would require SUVs and minivans to have a fuel efficiency of better than 18 miles per gallon if they are four-wheel drive, and 20-21 miles per gallon if two-wheel drive. Harbottle said the standard applies only to the purchase of new vehicles or when existing vehicles are repurposed. “If [the cars] aren’t available or aren’t practical, then the town doesn’t have to’’ adhere to the policy, Harbottle said. “It’s a policy that departments should be trying to do this.” Selectmen postponed voting on the new guidelines at their Tuesday meeting, but are likely to revisit the subject in early February.