WASHINGTON — Sen. Maria Cantwell announced late Thursday that she intends to support regulatory reform, giving a boost to the bill's prospects in the Senate, which plans to take up the legislation later this month when Congress returns from a Fourth of July recess.

The Washington Democrat's support comes at a critical time for the bill. The Senate had originally been expected to take it up this week, but votes for the legislation were thrown in doubt over Republicans' objections to a budget offsetting mechanism and the death of Sen. Robert Byrd, D-W.VA.

The two factors caused delays that prompted the regulatory reform conference to reconvene Tuesday to substitute a new mechanism to pay for the bill designed to be more palatable to the GOP.

The move by Cantwell is emblematic of the regulatory reform debate, which has been a rollercoaster of ups and downs. Earlier Thursday, observers were openly questioning whether support for the bill could collapse over the congressional break as lawmakers have more time to be lobbied on the bill.

To pass in the Senate, where Democrats controlled 59 seats before Byrd's death, the bill needs 60 votes — at least to overcome procedural hurdles to wrap up debate and prevent filibuster. Cantwell's switch to a ‘yes' brings Democratic leaders and the Obama administration one vote closer to victory on a major financial services overhaul.

When the Senate passed an earlier version of the bill in May, Cantwell and another Democrat, Sen. Russ Feingold of Wisconsin, opposed the legislation, arguing it did not go far enough.

Cantwell said Thursday she decided to switch because the bill had improved in conference.

"I will vote in support of the conference report because it makes great strides toward our ultimate goal: bringing all standard derivatives onto exchanges and clearinghouses, with aggregate position limits and strong anti-manipulation tools," Cantwell said in a press release.

Four Republicans also supported the bill in the Senate previously.

On Wednesday, Republican Sen. Susan Collins of Maine announced she would support the bill again.

When Byrd's seat is filled, his successor is considered likely to support it too, although Feingold has announced he remains opposed to the legislation. If Democrats hold the rest of the members of their party, they will still need to nail down one more vote to reach 60.

Of the Republicans who supported the bill previously, Sens. Scott Brown, Chuck Grassley and Olympia Snowe remain uncommitted. Snowe, who frequently gives Democrats a decisive vote and won several small business provisions in the legislation, is considered the most likely to support the bill again.

The House passed the final version of the bill on Wednesday. Passage in the Senate would be the last hurdle before President Obama could sign the bill into law.