Lockheed Martin employees are seen at work in 2009 in the company's NexGen Cyber Innovation & Technology Center. (HO/REUTERS)

Senators voted 52 to 46 in favor of the bill, coming up short of the two-thirds majority necessary to advance the bill to final passage. Failure to pass the measure further stalls years of bipartisan efforts to establish stricter security standards and, experts say, could leave the nation vulnerable to widespread hacking or a serious cyber attack.

“This is one of those days when I fear for our country and I’m not proud of the United States Senate,” Sen. Joseph I. Lieberman (I-Conn.), one of the bill’s chief sponsors, said ahead of the vote. “We’ve got a crisis, and it’s one that we all acknowledge. It’s not just that there’s a theoretical or speculative threat of cyber attack against our country — it’s real.”

In hopes of moving the bill forward, the White House and Democratic and Republican sponsors of the measure had agreed to weaken the proposal by making stricter security standards voluntary, instead of mandatory, for the large private firms that control most of the nation’s infrastructure.

On Wednesday, Gen. Mike Dempsey, the chairman of the Joint Chiefs of Staff, and White House counterterrorism adviser John O. Brennan voiced support for the measure. President Obama even authored a rare Wall Street Journal op-ed in favor of the bill, in hopes of garnering enough votes.

But even voluntary standards are opposed strongly by many in the business sector — and the Senate proposal would need to be reconciled with a House bill that lacks any mention of standards and that focuses instead on the exchange of cyberthreat data between industry and government.

In a statement, the White House blasted Thursday’s vote. “Despite the president’s repeated calls for Congress to act on this legislation, and despite pleas from numerous senior national security officials from this administration and the Bush administration, the politics of obstructionism, driven by special interest groups seeking to avoid accountability, prevented Congress from passing legislation to better protect our nation from potentially catastrophic cyber-attacks,” White House press secretary Jay Carney said.

The challenge surrounding cybersecurity is that most of the nation’s vulnerable systems — the computer networks that run the nation’s power, water, banking, transportation and communications — are overseen by the private sector. Legislators have sought to strike the right balance between regulating the private sector and encouraging companies to voluntarily tighten security measures.

Sen. Jay Rockfeller (D-W. Va.), another longtime cybersecurity safety advocate, called Republican opposition to the measure “reckless.”

“We worked hard for more than three years and now, because a handful of Republican senators are afraid of crossing the Chamber of Commerce’s beltway lobbyists, we may end up with nothing on this urgent issue,” Rockfeller said Thursday.

Republican critics of the bill argue that any cybersecurity standards — whether mandatory or voluntary — would place a financial strain on private companies. They say government intervention isn’t necessary on this issue.

Opponents also voted against the bill because Senate Majority Leader Harry M. Reid (D-Nev.) denied them an opportunity to propose related amendments and because the bill — drafted quickly by its Democratic and Republican cosponsors — never went through the normal committee process.

“We all recognize the problem. That’s not the issue here,” Senate Minority Leader Mitch McConnell (R-Ky.) said Thursday morning. “This is a big, complicated, far-reaching bill that involves several committees of jurisdiction,” he added. “Democrat leaders haven’t allowed any of these committees to improve the bill or even vote on it.”

But Reid also balked at proposed Republican amendments to the bill unrelated to cybersecurity, including an attempt by Sen. Mike Lee (R-Utah) to amend the bill with a ban on late-term abortions in the District of Columbia.

Congress is slated to leave Friday for a month-long congressional recess, and supporters couldn’t immediately say when the issue may be brought up again for a vote. Reid voted against the measure, reserving the right as Senate leader to reintroduce the measure at a later date.

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Ellen Nakashima contributed to this report.

Follow Ed O’Keefe on Twitter: @edatpost

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