* Group backs Cameron's call for new British role in Europe
* More than 500 business figures support campaign
* They want looser ties; debate widens before 2015 vote
* PM's pledge to claw back powers angered EU leaders
LONDON, April 22 (Reuters) - Prime Minister David Cameron won the support of 500 business leaders on Monday in his campaign to renegotiate Britain's ties with the European Union, a political gamble that has infuriated some of the bloc's biggest members.
Business for Britain, a new lobby group, said it backed Cameron's plan to repatriate powers from Brussels and hold a referendum on Britain's EU membership, provided his Conservative Party wins the next election.
France and Germany have attacked Cameron's stance, saying they will block any attempts by London to "cherry pick" EU policy. The United States has said it wants Britain to remain inside the EU.
Other business groups say the referendum pledge risks creating uncertainty that will deter investment, isolate Britain and stifle the stagnant British economy.
However, the new lobby group said cutting regulation, scrapping a planned financial transaction tax and allowing looser ties between its 27 members would benefit Britain and boost growth across a continent shaken by a debt crisis.
"Many would have you believe that business doesn't want politicians to try and renegotiate a better deal from Europe," said Alan Halsall, the group's co-chair and chairman of Silver Cross, a company that makes baby products. "Jobs and economic growth depend on a more flexible, looser relationship with the EU."
Since Cameron came to power in 2010, the long and bitter debate over Britain's place in Europe has resurfaced. Groups on both sides of the argument have begun drawing up battle lines before an election due in 2015.
Cameron, who wants to stay inside the EU, trails the Labour Party in the polls and is threatened by the UK Independence Party, an increasingly popular anti-EU group wooing disgruntled Conservatives.
The British leader is under pressure to appease Conservative lawmakers who want him to take a tougher line with Brussels, seen by euro sceptics as a wasteful, interfering bureaucracy eroding British sovereignty.
On the other side of the debate, the pro-EU camp says close ties with the EU, Britain's biggest trading partner, are vital at a time of intense global competition.
Among the 500 signatories of a letter sent by Business for Britain to newspapers to launch its campaign were Simon Wolfson, chief executive of retailer Next Plc ; Stuart Rose, chairman of online retailer Ocado Group Plc, and Richard Burrows, chairman of British American Tobacco Plc .
Business for Britain describes itself as an independent, cross-party group funded by donations from business supporters.
A poll last week for the British Chambers of Commerce, a lobby group that represents more than 100,000 companies, suggested some support for the group's position.
Nearly two-thirds of those polled (64 percent) said Britain's economic prospects would improve if it stayed inside the EU on renegotiated terms.
Sixty percent said withdrawal would be bad for business and the economy; 18 percent said it would have a positive impact.