LONDON — The British government said Monday that it would no longer pay a universal child subsidy to wealthier families, opening a campaign that may end up transforming Britain’s welfare system by reducing benefits to the middle and upper classes.

The decision, announced by George Osborne, the chancellor of the Exchequer, at the Conservative Party conference in Birmingham, departs from the Tory campaign promise to not place income restrictions on this hugely popular benefit and represents perhaps the most direct attack yet on the rich menu of broad-based entitlements that have underpinned European welfare states.

The government is scheduled to disclose on Oct. 20 how it intends to cut about $130 billion in spending over the next four years, cuts intended to sharply narrow a budget deficit that, at 11 percent of G.D.P., is one of the biggest in the world.

The exercise has been fraught with political infighting among Tories and with their governing coalition partner, the left-leaning Liberal Democrats, who have argued that middle-to-upper-income Britons should bear more of the brunt of welfare cuts than those who are poor or jobless.