Michael Gove and Philip Hammond would vote for Britain to leave the EU
Defence Secretary Philip Hammond has become the second cabinet minister to say he would vote for Britain to leave the EU if a referendum were held now.
But, like education secretary Michael Gove, he said David Cameron must be given a chance to bring powers back from Brussels before deciding.
Mr Hammond told BBC Radio 5live it would be "defeatist" to leave the EU without attempting reform.
Mr Cameron has pledged to hold a referendum in 2017.
"If the choice is between a European Union written exactly as it is today and not being a part of that then I have to say that I'm on the side of the argument that Michael Gove has put forward," said Mr Hammond in an interview on Radio 5live's Pienaar's politics.
Earlier, Mr Gove became the most senior Conservative to date to publicly contemplate backing Britain's exit from the EU, although "friends" of the cabinet minister have previously told a newspaper that is where he stands.
'Letting off steam'
"I am not happy with our position in the European Union but my preference is for a change in Britain's relationship with the European Union," said Mr Gove.
"Life outside would be perfectly tolerable, we could contemplate it, there would be certain advantages."
Tory backbenchers have tabled an amendment to the motion welcoming the Queen's Speech regretting the absence of legislation paving the way for a referendum in the government's plans for the year ahead.
Mr Gove described this as "letting off steam".
And he said he planned to abstain if there was a Commons vote on the amendment.
"My own view is let the prime minister lay out our negotiating strategy, make sure he has a majority, which I am convinced he will secure at the next election, and let's have the referendum then."
Home Secretary Theresa May also said she would abstain in the Commons vote, which will be held on Tuesday or Wednesday if it is called by Speaker John Bercow.
Mr Hammond said: "I believe that we have to negotiate a better solution that works better for Britain if we are going to stay in and play a part in the European Union in the future, but let me be absolutely clear: I think it is defeatist to sort of say we want to leave the European Union.
"We should say no, this is a club that we are members of, and before we talk about leaving it, first of all we're going to try and change the rules and change the way it works and change the objectives that it has in order to make it something that works for Britain."
David Cameron has promised an in/out referendum in 2017 - if the Conservatives win the next election.
A group of Conservative backbenchers, led by John Baron, have been campaigning for him to firm up this commitment by legislating in the current Parliament for a referendum.
The rebel MPs wanted the legislation to be included in last week's Queen's Speech setting out the government's plans for the year ahead.
Mr Cameron has said he was prevented from doing so by the Lib Dems.
So the rebels have taken the unusual step of tabling an amendment to the Queen's Speech debate, raising the prospect of government MPs voting against their own programme. It is thought about 100 backbench MPs could do so.
The amendment, tabled by Mr Baron and fellow Eurosceptic Peter Bone, expresses regret that the government has not announced an EU referendum bill.
It is highly unlikely to be passed, as Labour, the Lib Dems and many Conservatives will vote against it or abstain but Mr Baron has said it will keep the issue in the spotlight.
The furore has been seized on by Labour as a sign that Mr Cameron has lost control of his party.
The Conservatives say Mr Miliband is unwilling to give the public a say on a vital issue.
Speaking on Sky's Murnaghan programme, shadow chancellor Ed Balls said: "I don't think we should set our face against consulting the British people."
He said Labour would back a referendum if there was "any proposal to change the powers between Britain and the European Union which would take powers away from Britain".
But he said the party would not make a commitment to a referendum at a time when there was a push to reform the EU as it would be "destabilising" and not "statesmanlike".