WASHINGTON (CNN) -- Senate Republican leaders Friday threatened to block the Senate from taking up a bill that would put the chamber on record disagreeing with President Bush's troop increase in Iraq unless Democrats agree to allow Republican to offer alternatives to the measure.

The filibuster threat sets up a high stakes stand-off between the parties ahead of a Monday afternoon vote when 60 votes are needed for the Senate to begin debate.

At issue, according to a senior Republican leadership aide, is whether the Republicans will be allowed to offer at least two alternatives of their choice to the bill sponsored by Sen. Carl Levin, D-Michigan, and Sen. John Warner, R-Virginia and whether 60 votes will be required for any measure to pass, something that in this case could be strategically advantageous to Republicans.

"What we're interested in is having a process negotiated with the majority under which there will be a series of different alternatives which, as with virtually everything in the Senate, is subject to the 60 vote rule," Republican Leader Mitch McConnell said at a news conference.

"They have already rejected three compromises that would permit the Senate to vote on the President's plan," Democratic Leader Harry Reid said in a statement. "This obstructionism is an abdication of their responsibility to the American people on the most important issue facing our nation today."

"If the Republicans want to talk this weekend, we'd be happy to," said a senior Democratic leadership aide.

One of the alternatives the Republicans would likely offer is a proposal sponsored primarily by Sen. John McCain which establishes benchmarks to measure future progress of the Iraqi government. But the Republican aide wouldn't say what the second measure would be but suggested it might be aimed at splitting the Democratic caucus to show Democrats are not unified on the war.

If the parties reach an agreement there won't be a vote Monday and the Senate will move directly to the bill. But if a vote on the filibuster is required, all Republicans will vote in favor of it, McConnell said. For their part, all Democrats -- even the two announced opponents of the Levin-Warner bill -- are expected to vote to end the filibuster.

If Democrats can't vote to end the filibuster, they might be forced to pull the bill from the floor until they can reach an agreement with the Republicans.

Aside from the vote on the filibuster, the outcome of a final vote on the Levin-Warner bill remained too close to call Friday because several senators from both parties still have not announced their intentions.