FACTBOX-Comparison of US House, Senate climate bills

Oct 6 (Reuters) - Democrats in the U.S. Senate have sketched out their version of a climate change bill they plan to work on in coming weeks.

Many Senate details still need to be decided. But the legislation proposed by Senators John Kerry and Barbara Boxer embraces central elements of the bill passed in June by the House of Representatives, which attempts to reduce U.S. emissions of carbon dioxide and other greenhouse gases blamed for global warming.

Here are key similarities and differences between the two measures, which are a long way from being enacted into law:

* CAP AND TRADE: The House-passed bill and the Senate proposal both have cap and trade at their core. Under the system, the federal government would put limits, continually declining, on the amount of carbon pollution from stationary sources. Companies would need an annual permit for every ton of carbon pollution they release into the atmosphere. Utilities and factories that don't use all of their permits could trade, or sell them, to companies that need more.

* EMISSION REDUCTIONS: The Senate shoots for a 20 percent cut in smokestack pollution by 2020. The House-passed bill sets a 17 percent reduction from 2005 levels. Some moderates in the Senate undoubtedly will try to lower the goal to 14 percent.

Both bills have the same long-term goals: an 83 percent cut in U.S. carbon pollution by 2050.

* EPA POWERS: The Senate proposal would leave the U.S. Environmental Protection Agency with powers to further regulate greenhouse gas emissions, while the House-passed bill does not.

* FREE POLLUTION PERMITS: Eighty-five percent of the pollution permits companies would have to obtain would initially be given away by the government, with 15 percent sold, under the House bill. In 2026, many of the free permits would begin switching to those that must be sold. While some analysts have said the Senate bill would have a 75 percent-25 percent split between free versus auctioned permits, Senator John Kerry told Reuters his bill will end up being very similar to the House bill on this point.

* ALLOCATION OF PERMITS: The Senate bill does not settle the controversial question of how many free permits key industry sectors will get. Lobbyists and Senate staff are in the midst of those negotiations. This was a tough battle in the House, which ended up giving 30 percent of all free permits to local electric distribution companies, 15 percent to cement, steel, glass and other big energy-using firms, 9 percent to local natural gas distributors, 3 percent for companies making electric and advanced technology vehicles and 2 percent for oil refiners.