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* Goldman, JPMorgan make large donations to in campaign
* Morgan Stanley also likely to make a donation - source
* Cameron tells businesses: speak up about EU benefits
* Cameron hopes for deal in February, says not there yet (Adds likely Morgan Stanley donation, Cameron remarks)
By Sinead Cruise and William James
LONDON, Jan 21 (Reuters) - Goldman Sachs and JPMorgan aremaking large donations to the campaign to keep Britain insidethe European Union, sources said, highlighting the concern amongsome of the world's biggest banks over the impact of a Britishexit.
Goldman Sachs has agreed to donate a "substantialsix-figure sum" according to one source, while JPMorgan was preparing to make a similar donation, another sourcefamiliar with the matter said.
Another U.S. bank, Morgan Stanley, is also likely to makedonation but has yet to decide a sum to contribute, a sourcesaid. The bank declined to comment.
In the face of growing Euroscepticism among the Britishelectorate and political pressure from within his own party,Prime Minister David Cameron has promised to hold a referendumon Britain's EU membership by the end of 2017.
On Thursday, Cameron urged business leaders at the WorldEconomic Forum in the Swiss resort of Davos to speak up aboutthe benefits of Britain staying in a reformed EU.
Cameron is hoping to head off the threat of a British exit,or 'Brexit', by negotiating a deal on reforms to the bloc thataddress concerns about immigration, sovereignty andcompetitiveness at an EU summit next month.
He received some support on Thursday from French PresidentFrancois Hollande, who said none of Britain's EU reform demandswere "insurmountable", but that they must not prevent the eurozone from pursuing further integration.
Cameron said very good progress had been made with the EUbut that they were "not there yet".
With British public opinion finely balanced andrenegotiations with Cameron's EU peers meeting resistance,multinational businesses in Britain are facing up to the riskthat the vote could sever links with the country's biggesttrading partner.
The donations by three heavyweight U.S. banks with heavyEuropean presence reflect the financial sector's acute concernsthat Britain's role as a global financing hub and major tradingcentre for the euro could be under threat if it gives up itsmembership.
British banks were more circumspect in pledging theirsupport. A source familiar with Barclays said the firmhad a policy not to make political donations, while a sourcewith knowledge of Royal Bank of Scotland said the bankwas waiting for clarity on the government's position.
"THE ESTABLISHMENT"
A spokesman for pro-EU group Britain Stronger in Europe, theexpected recipient of the donations, said it had a broad rangeof backers: "This includes many small donors, philanthropistsand businesses worried by job losses and price rises if we wereto leave."
Until a date for the referendum is set, campaigns on bothsides can accept and spend donations without restriction.However they may be required to declare details of prior donorsonce the government sets a referendum date. Spending will becapped during the period immediately before the referendum.
The donations were dismissed as "no surprise" by Leave.EU,one of several pro-Brexit campaigns, which says the EU worksagainst ordinary Britons and protects vested political andcommercial interests.
"The referendum will be a campaign of the British peopleagainst the establishment of international bankers,multinational corporate tax dodgers and out-of-touchpoliticians," said Arron Banks, the group's co-founder.
Arch-Eurosceptic Nigel Farage, leader of the UK IndependenceParty whose popularity put pressure on Cameron to make the offerof a referendum, described the donations as "the unholy allianceof big banks and big politics."
Cameron, however, is keen to enlist the support ofbusinesses to help his reform agenda clear political hurdles inother European capitals, and to illustrate the damage that hebelieves leaving the bloc would do to the country's economy.
"If business backs my reforms ... I would argue get outthere and support those things," he said in Davos.
"The sooner you can start to look at your own businesses andcome up with the examples and the ideas about the benefits andthe problems that there are with Europe the more that you areable to help to explain and set the context for this vitallyimportant question." (Additional reporting by Elizabeth Piper in Davos, RachelArmstrong and Kylie MacLellan in London, Writing by WilliamJames; Editing by Guy Faulconbridge/Jeremy Gaunt)
