But if it fails, Republicans are prepared to bring the entire bill down on a point of order, rather than let it move ahead with the extra $15 billion added by Appropriations Chairman Byrd but opposed by the President.
Sen. Mike Crapo, R-Idaho, called today's expected floor standoff "a test of nerve here," between those who want to "bust the budget" and those who want to use Senate procedures to stop them.
"At one point or another, there has to be some sort of compromise or some sort of concession," Crapo said.
Under a unanimous consent resolution reached Wednesday night, the Senate will set aside work on the farm bill and take up the Defense spending bill at noon today.
Following a GOP strategy session Wednesday, Sen. Olympia Snowe of Maine said Republicans were "identifying some of the areas that are important to homeland security" in Byrd's add-on that could be included in a compromise.
Texas Sen. Kay Bailey Hutchison said, "I hope we can negotiate something the President is comfortable with," but insisted Republicans would not exceed $20 billion in supplemental funding.
Byrd's package contains the regular $317 billion Defense appropriation, plus the $20 billion supplemental that represents Congress' half of the $40 billion approved after Sept. 11. Byrd's package also contains another $15 billion--$7.5 for domestic recovery aid and $7.5 billion for "homeland security."
Although Budget ranking member Pete Domenici, R-N.M., said the GOP floor strategy was "evolving," a leadership aide said Republicans hoped to offer an alternative consisting of the $317 billion Defense bill, plus a version of the $20 billion supplemental that would mirror the House version while making room for some of Byrd's extra homeland security spending.
Sen. Robert Bennett, R-Utah, said the challenge was to find a way to meet Byrd's "legitimate concerns for homeland security" and President Bush's "legitimate desire to see that those concerns are properly analyzed and authorized before we start appropriating money."
Bennett said he hoped Byrd would start talking to the administration directly to avoid a veto of the Defense bill.
But Byrd indicated Wednesday that he is not ready to back down, defending the extra money as a necessary response to real threats. Byrd called on Senate colleagues and the administration to put the country's needs over partisan politics.
Byrd also called "mind-boggling" the White House position that Congress should wait for Bush to request another supplemental in the spring.
On Wednesday evening, Republicans had not determined their final floor strategy, although one Senate GOP aide said there was "zero doubt" that they have the 41 votes to sustain any of the 60-vote points of order they could raise against the bill.
Those include objections because the bill exceeds its subcommittee allocation, exceeds the statutory cap, uses the emergency designation and includes language within the Budget Committee's jurisdiction but not considered by the committee.
Although Republican leaders have not shown any signs of flinching, several Republicans have expressed general concern about increased spending as the session wraps up.
"We're getting carried away with spending," said Sen. Wayne Allard, R-Colo. "I'm afraid that we're passing too much legislation in haste, and that we will regret this two or three years down the road."
Also Wednesday, House and Senate negotiators agreed to increase intelligence spending by 8 percent, with an emphasis on rebuilding traditional human spy networks and boosting analysis of raw data so they will be useful to America's war against terrorism, the Associated Press reported.
Both the House and Senate must vote on the final version of the intelligence authorization bill before it becomes law. Senate Intelligence Chairman Graham said he hopes that will happen this week.
Brody Mullins contributed to this report.