WASHINGTON — A bipartisan group of leading senators has reached agreement on the principles for a sweeping overhaul of the nation's immigration laws, including a path to citizenship for the 11 million illegal immigrants already in this country.

The deal, to be announced at a news conference Monday, also covers border security, non-citizen or "guest" workers and employer verification of immigration status.

Although thorny details remain to be negotiated and success is far from certain — the legislation could run into trouble in the Republican-controlled House — 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.