WASHINGTON -- A key House committee close to Speaker John Boehner (R-Ohio) gutted crucial provisions of a National Security Agency surveillance reform bill on Tuesday. The move dismayed civil liberties advocates, some of whom immediately withdrew their support ahead of a Thursday floor vote.

"The bill has been watered down far, far down even from the compromise that was struck when the bill was voted out of committee," said Patrick Toomey of the American Civil Liberties Union. "While it represents a slight improvement from the status quo, it isn't the reform bill that Americans deserve."

The new version of the NSA bill presents reform advocates with a difficult choice: hold out hope that a companion Senate bill can nudge reform in their direction, or to oppose all efforts at changing the NSA now. In 2015, the provision that underlies the agency's controversial call records program is set to expire, so if no bill is passed before then, the program will end.

One key alteration to be approved Tuesday by the House Rules Committee seems to significantly expand which "selection terms" can be used to compel phone companies to turn records of Americans' calls over to the government. Bulk phone metadata collection was the first program revealed from documents leaked by former NSA contractor Edward Snowden, and perhaps the most controversial.

The new version of the bill retains some significant reforms to the call records program. The spy agency will still be prohibited from collecting the data in bulk directly, and the Foreign Intelligence Surveillance Court will still approve requests for phone records data from the telecoms. But the House Rules version of the bill loosens tougher restrictions on the NSA passed two weeks ago by the House Judiciary and Intelligence Committees, and critics say in particular that the expansion of the call records search terms will seriously undermine those steps forward.

New language in the bill only suggests that the NSA's searches may be limited to terms "such as a term specifically identifying a person, entity, account, address, or device." The vagueness of that "such as" language worries advocates.

"Any time they introduce ambiguity, which is what these changes do, that is a very worrying thing for us, because that is what got us here in the first place," said Toomey. "Without there being a more precise definition, it seems like they're opening the door to very bulky collection."

Another change to the NSA reform bill lowers the amount of reporting that telephone and internet companies may provide to the public about government data requests. Advocates had seen those transparency procedures as the canary in the coal mine for government overreaches. In the new version of the bill, the transparency standards mirror those the Justice Department has already agreed to with telecoms.

The new version of the bill is expected to pass out of the House Rules committee Tuesday night.

The ACLU pledged to fight for floor amendments to strengthen the bill's privacy protections. And other groups, including Access and the New America Foundation's Open Technology Institute, withdrew their support for the legislation.

At the same time, the changes introduced by the House Rules Committee do not seem to have deterred some of the staunchest advocates for NSA reform. The new version of the legislation was offered in the Rules Committee by Rep. James Sensenbrenner (R-Wis.), as well as Democratic Reps. John Conyers (Mich.), Jerrold Nadler (N.Y.) and Bobby Scott (Va.), all of whom supported a stronger version of the reform measure, the USA Freedom Act, that passed the House Judiciary committee.

Some outside Congress suggested that House leadership and President Barack Obama's administration placed significant pressure on legislators to weaken their reforms. Spokespersons for John Boehner and the White House National Security Council did not immediately respond to a request for comment.

"House leaders should have allowed a vote on the compromise version of the USA Freedom Act that was already agreed to, rather than undermining their own members and caving in to the intelligence community's demands," said Kevin Bankston of the New America Foundation, a public policy group, in a statement.

"We're gravely disappointed that rather than respecting the wishes of the unanimous Judiciary and Intelligence Committees, the House leadership and the Obama Administration have chosen to disrupt the hard-fought compromise that so many of us were willing to support just two weeks ago."