A bipartisan group of leading senators has reached agreement on the principles of sweeping legislation to rewrite the immigration laws of the United States.

The deal, which was scheduled to be announced on Monday afternoon, covers border security, guest workers and employer verification, as well as a path to citizenship for the 11 million illegal immigrants already in the country.

Although thorny details remain to be negotiated and success is far from certain, the development heralds the start of what could be the most significant effort in years toward overhauling the nation's inefficient patchwork of immigration laws.