By Andrew Osborn
LONDON (Reuters) - Britain's Queen Elizabeth set in motion Prime Minister David Cameron's plans for a European Union membership referendum on Wednesday as he faced pressure to explain when it will be held and what changes to the EU he wants beforehand.
Cameron, who says he would prefer to stay inside a reformed EU but isn't "ruling anything out" if it fails to change, was re-elected on May 7 on a pledge to reshape ties with the bloc before allowing Britons to vote on whether to stay or leave.
Donning her crown as she sat on a gilded throne in a packed House of Lords, the 89-year-old queen outlined the referendum plans in a speech written for her by Cameron's Conservative government as she opened parliament with a customary display of pomp.
"My government will renegotiate the United Kingdom's relationship with the European Union and pursue reform of the European Union for the benefit of all member states," the queen told an audience made up of politicians and lords clad in crimson robes trimmed with white ermine.
"Alongside this, early legislation will be introduced to provide for an in-out referendum on membership of the European Union before the end of 2017."
The law will be introduced into parliament on Thursday as Cameron begins a European tour to try to charm sometimes reluctant counterparts into endorsing EU reform.
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The tour will include talks with French President Francois Hollande in Paris and German Chancellor Angela Merkel in Berlin.
Cameron has said he would be ready to hold the referendum before 2017 if he completes the renegotiation early, something some pro-EU campaigners advocate. But he is under pressure from some of his own Eurosceptic lawmakers who want him to ask for more and to take his time reaching any settlement.
Some EU politicians have complained they do not know enough, beyond what they say are broad and nebulous goals, about what it is Cameron wants to change. He says he wants to decouple Britain from the EU's official aim of "ever closer union" and to be able to restrict EU migrants' access to Britain's welfare system.
Cameron is adamant that such changes would require re-opening the EU's founding treaties, something countries such as France are opposed to.
In a potential setback for the prime minister, a Franco-German paper seen by Reuters shows the two countries have agreed plans to strengthen cooperation among the 19 countries using the euro currency, without changing existing treaties.
The blueprint would bolster the euro zone, of which Britain is not a member, by holding more regular summits of its leaders and strengthening the Eurogroup forum of finance ministers.
Other laws Queen Elizabeth outlined on Wednesday included a crackdown on illegal immigration, more devolved powers for Scotland and a bill preventing any rise in key taxes before 2020.
A law to reform human rights legislation, designed to weaken the influence of the European Court of Human Rights, was not part of the package, however.
Cameron had not promised to immediately press ahead with the move, but his decision to tackle it later stoked speculation he wanted to avoid an early showdown over a plan that has divided his party.
(Additional reporting by William James, Kylie MacLellan and Estelle Shirbon; Editing by Guy Faulconbridge/Mark Heinrich)