Labour leadership contender Liz Kendall has said the policy of removing tax credits to migrant workers is "definitely something we should look at" but called for a wider debate on Britain's future in the EU.
She accused the Prime Minister of putting "internal political management" ahead of the country's national interest.
Ms Kendall told BBC 1's The Andrew Marr Show: "We do have to deal with the issue of people who come here to work. They must be working and not claiming benefits. But this is about something much bigger - it is about the future of our country and our place in the world.
"David Cameron should be focusing on what is in Britain's national interest and our place in the world, not on internal party politics."
Asked if she was in favour of removing tax credits to migrant workers, she replied: "That's definitely something we should look at, but this is a far bigger debate.
"Of course David Cameron is reducing the question because he has failed to show leadership with his own backbenchers.
"He has allowed this to define whether or not Britain remains part of Europe. That is a profound lack of leadership on his behalf because he is more concerned about internal political management than the future of the country."
Pushed on the migration question again, she added: "I'm in favour of free movement of labour but not free movement of benefits. People who come here should come here to work.
"If we allow this debate to be defined by that issue alone, we will be profoundly wrong. This about Britain's place in the world, our future economy."
She reiterated her support for maintaining the 2% defence spending commitment, adding: "Our place in Europe is essential as part of our wider international relationship."
Ms Kendall also failed to confirm whether or not she supports the £3 billion of cuts announced by the Chancellor this week.
Asked about the need to cut the deficit, she said: "Let's see what the Conservatives come out with in their budget. I'm not going to provide a budget response to a budget that has not been delivered
"But it is vital that fiscal credibility is at the heart of all we do because people need to trust us with our money to win but also because there is nothing progressive about spending more on debt interest repayments than spending on the future of educating our children."
Asked again whether the deficit needs to be dealt with, she replied: "The deficit needs to be dealt with, but we need to do far more....this is the really important challenge for the future. How do we get jobs and growth in every part of the country?"
Asked if she supports cuts as a means of getting the deficit down, she said: "We need to balance the books and live within our means but in a better, fairer way.
"When we have seen what George Osborne is proposing I will come back to you.
"Let's see what the details are. We have yet to see many of the commitments that the Conservatives made during the campaign.
"Fiscal credibility and responsibility and living within our means is essential but so too is making sure we have real growth in all parts of the country. Ed Miliband was actually right about that as a big challenge."
Asked if she had enough "heft" to be Labour leader, Ms Kendall replied: "Yes, I do.
"The question for this leadership election is not what jobs people have had in the past but who will face up to what we need to do to win in 2020 to change our country."