Under intense pressure from immigrant groups and the White House, the Senate yesterday narrowly approved a motion to debate the immigration overhaul bill, the first in a series of votes that will test whether the 110th Congress will be able to clear the sweeping measure.

By surpassing the 60-vote threshold with a 64-35 vote, the Senate now moves to consider about two dozen amendments and will attempt to have a final vote to cut off debate Thursday. Many of the amendments are considered poison pills that could kill the compromise bill, which was negotiated by a bipartisan coalition and the White House.

Still, supporters heralded yesterday’s vote as a “major step forward” that showed the tide was turning on the immigration bill, which Majority Leader Harry Reid (D-Nev.) had pulled from the Senate floor earlier this month after it fell 15 votes shy of cutting off debate.

“I’ve been in Congress for more than 40 years and immigration reforms are always controversial,” the lead Democratic negotiator, Sen. Edward Kennedy (Mass.), said. “But Congress is expected to muster the political will to get it done. And today, I’m proud to say that we did.”

President Bush and top administration officials launched a renewed campaign yesterday to pressure hesitant Republicans to push the measure through.

“I view this as an historic opportunity for Congress to act, for Congress to replace a system that is not working with one that we believe will work a lot better,” Bush said at a briefing yesterday morning with the business community.

Still, significant opposition exists. Hard-line conservative critics of the bill say they will use all tools available to them to delay and possibly derail the bill, which would provide a pathway to citizenship for the nation’s 12 million illegal immigrants, create a temporary guest-worker program, overhaul how immigrants are selected for visas and add new border security measures.

“I’m going to do everything that I can do to make sure that this bill never leaves the Senate,” Sen. Tom Coburn (R-Okla.) said. “There are a lot of things that we haven’t used yet that we haven’t used in hundreds of years around here, that are going to come up.”

Earlier yesterday, Coburn joined House Republicans in an unusual press conference in the Senate to criticize the pending bill. The House GOP argued that there was strong opposition within the caucus for the Senate bill, underlining the steep climb supporters face in trying to push the measure through the lower chamber.

“The House Republican conference disapproves of the Senate bill,” Rep. Pete Hoekstra (R-Mich.) said.