* G7 pledges to complement EU energy security plan
* European Commission links energy security, climate debate
* U.S. goals face domestic political opposition
* European Union struggling to convince Poland
By Barbara Lewis
BRUSSELS, June 5 (Reuters) - The world's leading industrialised nations gave their backing on Thursday to a new global deal on climate change in 2015 after promises from the United States at the start of the week galvanised flagging momentum.
The United States' plan to cut emissions from power plants by 30 percent by 2030, which will run into domestic opposition, prompted the European Union into a defence of its own record.
China, the world's biggest emitter of greenhouse gases, also gave a hint that it would set some kind of cap on its emissions.
A draft of the G7 communique seen by Reuters said the leaders affirmed their "strong determination" to adopt a new global deal in 2015 that is "ambitious, inclusive and reflects changing global circumstances".
It said the G7 nations - Britain, Canada, France, Germany, Italy, Japan and the United States - remained committed to low-carbon economies and limiting temperature rises to 2 degrees Celsius above pre-industrial levels, the limit scientists say can prevent the most devastating effects of climate change.
The communique produced at a summit in Brussels also committed G7 nations to announce national contributions to reducing emissions by the first quarter of next year, ahead of a Paris conference on deciding a global deal in December 2015.
At the same time, the G7 offered the EU support with its efforts to make its energy supplies more secure, promising to "complement the efforts of the European Commission to develop emergency energy plans for winter 2014-2015".
In Europe, the quest for energy security in the face of threats from Russia that it could disrupt supplies of gas pumped through Ukraine, has knocked the climate debate down the agenda.
But addressing the G7 in Brussels, Commission President Jose Manuel Barroso said the two issues went "hand in hand".
EU nations say domestic, renewable sources, such as solar and wind, can reduce the need for fossil fuel imports from nations such as Russia, while Poland, which relies on polluting coal, says coal is a reliable, domestic fuel source.
Of the G7 nations, Japan and Canada have pulled out of the Kyoto process on tackling climate change. The United States signed but did not ratify the original treaty.
Republicans in Congress are expected to resist the latest U.S. proposals, but the plans can still help.
"I think it puts the United States in a strong position to lift up the need for international action heading into next year on concrete plans to reduce emissions," Ben Rhodes, deputy national security advisor, told reporters.
Connie Hedegaard, the EU Climate Commissioner, said the EU was still in the vanguard and would "substantially over-achieve" its targets for cutting greenhouse gas emissions by 2020, delivering more than its promised 20 percent cut versus 1990 levels.
"None of them wants to be perceived as the laggard, which is a good thing," Alden Meyer, of the Union of Concerned Scientists, said on the sidelines of preparatory talks for the 2015 deal in Bonn this week.
The United States' plans are for the U.S. power sector to cut CO2 emissions by 30 percent by 2030 from 2005.
In addition, it has an existing national goal, set in 2009, to cut emissions by 17 percent below 2005 levels by 2020, equivalent to 3.5 percent below levels in 1990 - the U.N. benchmark year - after a sharp rise in emissions in the 1990s.
Following on from its 2020 goal, the EU is trying to reach agreement on 2030 targets.
In January, the EU executive put forward the idea of 40 percent cut by 2030 and in March EU leaders gave themselves until October to agree on the target. (Additional reporting by Luke Baker, Roberta Rampton and Jeff Mason in Brussels and Alister Doyle in Bonn. Editing by Mike Peacock)