The Senate blocked efforts to water down a sweeping immigration bill coupling tougher border controls with a guest worker program similar to proposals spelled out by President George W. Bush.

The bill’s backers said they were encouraged about its prospects. But they said it faced an uncertain future in eventual negotiations with the House of Representatives, which earlier passed a tough bill that would turn illegal immigrants into felons and erect a big border fence.

“The signals we are getting are very good,” said Senator Ken Salazar, a Colorado Democrat. The Senate bill includes border security and enforcement measures but adds a guest worker program and a pathway to citizenship for some of the estimated 12 million illegal immigrants.

In a 69-28 procedural vote, the Senate killed an amendment proposed by Sen. Byron Dorgan, a North Dakota Democrat, that would have eliminated the guest worker program for future immigrants. It would have limited the program to illegal immigrants who have lived in America for at least two years.

The Senate also rejected a measure offered by Senator Johnny Isakson that would have required the Department of Homeland Security to certify that US borders.