THE federal opposition wants to lock Australia into a modest five per cent cut in greenhouse gas emissions under a plan which it says will cost much less than the government's ETS proposal.

But Prime Minister Kevin Rudd who's open to a larger cut if other nations also agree to bigger reductions .. says Opposition Leader Tony Abbott's plan is a climate con job.

Mr Abbott says his scheme would cost about three billion dollars in the first four years and would among other things involve farmers planting trees and the installation of solar panels.

The duelling climate schemes and targets are likely to offer a key difference at the federal election expected this year.