BERLIN - German Chancellor Angela Merkel said on Tuesday that she was growing nervous about the lack of progress at the U.N. Climate Conference in Copenhagen.

I can't conceal the fact that I've become a bit nervous about whether we'll be able to do it, Merkel told a news conference with Indonesia President Susilo Bambang Yudhoyono. We all know time is running out and we need to get serious.

Delegates from nearly 200 countries are in Copenhagen for the talks to hammer out a deal aimed at slowing global warming.

Merkel, who says Germany will commit to reduce greenhouse emissions by 30 percent from 1990 levels by 2020 or even 40 percent if others agree to steep cuts, will be in Copenhagen with world leaders for the last two days on Thursday and Friday.

It's well known that large conferences like this, with so many different interests, sometimes stall, she said. But considering how little time is left everyone needs to make a constructive contribution to make Copenhagen a success.

Yudhoyono, who hosted the U.N.-led talks in Bali two years ago and helped break a late deadlock there, will be acting as an informal co-chair in Copenhagen with Denmark, Merkel said.

We experienced ourselves in Bali what can be done with good will, Yudhoyono said. We have experience with deadlock situations. This is a window of opportunity. We all know that we cannot allow (a failure) to happen.

Indonesia, where deforestation and forest fires led to the World Bank naming it the world's third largest emitter of greenhouse gases, is seen as an important player in the fight against climate change.

Germany is the world's sixth largest emitter.

(Reporting by Erik Kirschbaum; editing by Dominic Evans)