WASHINGTON » The U.S. House today weighed whether to end the National Security Agency’s authority to collect hundreds of millions of Americans’ phone records as the fight pitting privacy rights against the government’s efforts to thwart terrorism got a new airing.

A showdown vote, expected late in the day, marked the first chance for lawmakers to take a stand on the secret surveillance program since former NSA systems analyst Edward Snowden leaked classified documents last month that spelled out the monumental scope of the government’s activities.

The issue created unusual political coalitions in Washington, with the Obama administration, national security leaders in Congress and the Republican establishment facing off against libertarian-leaning conservatives and some liberal Democrats.

With a flurry of letters, statements and tweets, both sides lobbied furiously in the hours prior to the vote in the Republican-controlled House. The director of national intelligence, James Clapper, warned against dismantling a critical intelligence tool.

Republican Rep. Justin Amash of Michigan, chief sponsor of the effort, said it was designed to end the indiscriminate collection of Americans’ phone records.

His measure, offered as an addition to a $598.3 billion defense spending bill for 2014, would cancel the statutory authority for the NSA program, ending the agency’s ability to collect phone records and metadata under the USA Patriot Act unless it identified an individual under investigation.

Amash stepped up the pressure on rank-and-file colleagues, looking ahead to meetings with constituents during next month’s congressional break.

"As you go home for August recess, you will be asked: Did you oppose the suspicionless collection of every American’s phone records? When you had the chance to stand up for Americans’ privacy, did you?" the Michigan Republican asked in a statement pleading for support for his measure.

Whatever the outcome in the House, the measure faces strong opposition in the Senate and from the White House and is unlikely to survive in a final spending bill.

Since the Sept. 11, 2001, attacks, Congress has authorized — and a Republican and a Democratic president have signed — an extension of the powers to search records and conduct roving wiretaps in pursuit of terrorists.

Two years ago, in a strong bipartisan statement, the Senate voted 72-23 to renew the Patriot Act and the House backed the extension 250-153.

Since the disclosures this year, however, lawmakers have said they were shocked by the scope of the two programs — one to collect records of hundreds of millions of calls and the other allowing the NSA to sweep up Internet usage data from around the world that goes through nine major U.S.-based providers.

"We’ve really gone overboard on the security side," said Rep. Peter Welch, D-Vt., who argued that the "vast surveillance grab" has come at the expense of Americans’ constitutional rights to privacy.

Welch said it was time for a full debate on behalf of American taxpayers about programs long cloaked in secrecy and part of an annual classified intelligence budget of about $30 billion.

Although Republican leaders agreed to a vote on the Amash amendment, one of 100 to the defense spending bill, time for debate was limited to 15 minutes out of the two days the House dedicated to the overall legislation.

The White House and the director of the NSA, Army Gen. Keith Alexander, made last-minute appeals to lawmakers, urging them to oppose the amendment. Rep. Mike Rogers, R-Mich., and Rep. C.A. Dutch Ruppersberger, D-Md., leaders of the House Intelligence Committee, implored their colleagues to back the NSA program.

Eight former attorneys general, CIA directors and national security experts wrote in a letter to lawmakers that the two programs are fully authorized by law and "conducted in a manner that appropriately respects the privacy and civil liberties interests of Americans."

White House press secretary Jay Carney issued an unusual, nighttime statement on the eve of today’s vote, arguing that the change would "hastily dismantle one of our intelligence community’s counterterrorism tools."

Proponents of the NSA programs argue that the surveillance operations have been successful in thwarting at least 50 terror plots across 20 countries, including 10 to 12 directed at the United States. Among them was a 2009 plot to strike at the New York Stock Exchange.

Rogers joined six GOP committee chairmen in a letter urging lawmakers to reject the Amash amendment.

"While many members have legitimate questions about the NSA metadata program, including whether there are sufficient protections for Americans’ civil liberties," the chairman wrote, "eliminating this program altogether without careful deliberation would not reflect our duty, under Article I of the Constitution, to provide for the common defense."

The debate over privacy and national security has prompted calls and emails to lawmakers, said Rep. Tom Rooney, R-Fla., a member of the Intelligence panel who said members of Congress are facing competing pressures.

The overall defense spending bill would provide the Pentagon with $512.5 billion for weapons, personnel, aircraft and ships plus $85.8 billion for the war in Afghanistan for the next budget year.

The total, which is $5.1 billion below current spending, has drawn a veto threat from the White House, which argues that it would force the administration to cut education, health research and other domestic programs in order to boost spending for the Pentagon.

In a leap of faith, the bill assumes that Congress and the administration will resolve the automatic, across-the-board spending cuts that have led the Pentagon to furlough workers and cut back on training. The bill projects spending in the next fiscal year at $28.1 billion above the so-called sequester level.

In addition to the vote on the Amash amendment, the House also will consider an amendment prohibiting any U.S. funds for military or paramilitary operations in Egypt and barring the administration from military action in Syria if that would violate the War Powers Resolution.

The overall bill must be reconciled with whatever measure the Democratic-controlled Senate produces.