It’s a rare area of agreement between Republicans and the Obama administration: The government should reduce its outsize role in making sure that people can buy homes. And yet, in the past three months, these officials and others in Washington have taken steps that expand the government’s support of the housing market. The reason is that the economy and the housing market, in particular, remain weak. Officials are worried that withdrawing government support for housing could make it more difficult for people to buy homes, reducing demand and sending housing prices even lower.