The Washington lawmaker who is leading efforts to reform US surveillance practices has warned European politicians that his legislation faces a difficult ride through Congress and resisted calls to expand the law by adding provisions to protect the privacy of foreigners.

Representative Jim Sensenbrenner told a meeting of the civil liberties and justice committee of the European parliament to focus hopes on diplomatic negotiations instead – pointing to a key Washington meeting next week, between EU commissioner Viviane Reding and US attorney general Eric Holder.

Sensenbrenner's testimony, thought to be the first by a US congressman before a committee of the European parliament, points to the difficulties that reformers in Washington face in assembling a coalition to push reform legislation though Congress.

Although recent revelations that the National Security Agency eavesdropped on foreign leaders have reignited the political debate over surveillance practices, it is not a feature of the key reform bill sponsored by Sensenbrenner and the Democratic Senator Patrick Leahy, which largely focuses on limiting the NSA's domestic powers to collect bulk data in the US.

Sensenbrenner, a Republican, has said that the bill, known as the USA Freedom Act, may also have to be attached to broader legislation, such as measures to approve annual funding for the intelligence community, in order to reach a floor vote and overcome procedural opposition.

"There is no question that for Senator Leahy and me to win, we have to fight the administration, the leadership of our respective parties and our respective houses of Congress as well as the intelligence committee members," Sensenbrenner told the committee in Brussels. "We hope to have it included in the money bill and we will try to attach it, particularly in the House where it will have more chance. The default position would be to defeat the money bill."

Sesenbrenner also attacked rival reforms proposed by the chair of the Senate intelligence committee, Dianne Feinstein, which he described as a "scary" attempt to expand the powers of the NSA.

"It codifies what the NSA has been doing under bulk collection – until now what they have been doing is because a court says yes, but the Feinstein bill puts what the NSA has been doing into law and says everything is OK.

"It also makes matters worse [for foreigners]. For 72 hours it sanctions warrantless surveillance of any foreigner who enters the US without getting any approval. Believe me, that is scary."

NSA director General Keith Alexander chats with Dianne Feinstein before a Senate intelligence committee hearing. Photograph: Jim Lo Scalzo/EPA

Sensenbrenner said he remained optimistic of passing real reform, pointing to the narrow defeat of earlier efforts to rein in the NSA.

"I think a very helpful sign was that the Amash amendment only failed by 12 votes and this was a wake-up call to folks in oversight that something is seriously wrong," he said. "That was three-and-half months ago, and since then there has now been more of a debate and a report by the inspector general that the NSA violated their own rules thousands of times.

"The real question is whether we can get a vote on our proposals in the House and Senate. I am very happy to have support from Senator Leahy, who is the Senate president pro-tempore and the fourth in line to the presidency."

Sensenbrenner's testimony was well received by European politicians who have been pressing for action on a host of privacy concerns, but it showed how little influence such figures have on US surveillance activity.

"It is evident that both the legal framework and the US constitutional systems make it extremely difficult to extend legal protection on privacy to EU citizens," said Claude Moraes, a London MEP and rapporteur for the committee on surveillance issues. "Whilst there is cross-political support for the US Freedom Act 2013, could I ask on whether there is support to strengthen safeguards for EU citizens, given the extent of the press reports into how the [Edward] Snowden documents have undermined trust in the transatlantic relations?"

Sensenbrenner was sympathetic but stressed that his focus would continue to be on US domestic reform. "I am not here to say that what I have proposed is a uniform law that can apply all around the world because it simply will not work because of various constitutional limits," the congressman said.

Instead, the committee discussed the threat of withdrawing intelligence co-operation or refusing to take part in trade talks as possible points of leverage over the US administration.

"International co-operation is crucial to stopping terrorism, but trust is also integral," said Sensenbrenner, in his prepared remarks. "I ask my friends here in the European Parliament to work pragmatically with the United States to continue balanced efforts to protect our nations. Together we can rebuild trust while defending civil liberties and national security on both sides of the Atlantic."