David Cameron has tried to outflank Labour by proposing that fathers be allowed more paid leave to look after babies if mothers want to return to work.
A Tory government would bring in more flexible "family-friendly" policies to allow more women to return to work after having children in the hope of closing the "pay gap" between the sexes.
The Tories will put measures to help families at the top of the agenda at their spring conference in Gateshead, which opens today. They will accuse the Government of imposing further burdens on hard-pressed families in this week's Budget.
Parental leave could become a key battleground between the two main parties at the next general election. Labour has announced plans to extend the period of paid leave from 39 to 52 weeks by 2010. The first 26 weeks would have to be taken by the mother but after that, the paid leave could be used by the father as long as the mother had returned to work.
The Tories argue that the Labour proposals are not flexible enough and want families, rather than the state, to choose how the system should work.
Their plans, published last night, would ensure the mother took the first 14 weeks, but the remaining 38 weeks could be taken by the father or simultaneously by both parents.
Mr Cameron told ITV News: "Why not let people make up their own minds about what's good for them? The world is changing, men want to be more involved in bringing up their children."
John Hutton, the Business Secretary, said the Tories' "big idea" showed how out of touch they were. "In reality very few families would be able to take advantage of offering paternity leave to both parents at the same time because this implies a major drop in family income at the critical moment in a new-born baby's life," he said.