WASHINGTON- House Democrats are outlining a plan to cut greenhouse gases by 20 percent over the next decade and 83 percent by mid-century.

But the draft proposal to be unveiled Tuesday leaves for future negotiations one of the most contentious issues: It does not say how pollution allowances would be distributed or whether they will be sold by auction or given away to polluting industries.

The so-called “discussion draft” also calls for increasing energy efficiency and requiring utilities to produce a fourth of their electricity from renewable energy sources by 2025.

The emission reductions mirror a proposal by President Barrack Obama.