A summer-long drumbeat of revelations about government online spying has put some of Silicon Valley's biggest companies in an increasingly uncomfortable bind: While national security rules limit what they can say, Google (GOOG), Facebook and other tech giants are struggling to reassure consumers and business customers that their information is secure.

Last week's reports about U.S. and British efforts to crack Internet encryption only added more pressure on the industry to distance itself from those government programs -- whether by quietly beefing up internal security defenses or publicly suing the United States government, say analysts and industry officials.

"Consumers are concerned. No matter what the companies say, the question is going to be: 'Is there something you're not telling us?' And they can't answer that question," said Daniel Castro, a senior analyst at the nonprofit Information Technology and Innovation Foundation. He estimates the spying revelations could cost U.S. tech companies up to $35 billion in lost revenue because of eroding customer trust.

Leading Internet companies pushed back this week, as Facebook and Yahoo (YHOO) followed Google and Microsoft in filing lawsuits that seek court permission to reveal more information about the quantity and kinds of data they have been required to share with the National Security Agency or other authorities.

In part, the companies say they want to show they're providing only a limited amount of data -- involving a small number of the billions of people who use their services -- and only in response to legal orders.

News reports about the NSA programs are causing "substantial harm to Google's reputation and business," the Internet search giant said in its latest court filing, which complained that those reports have included "many false and misleading stories" about Google's role in government surveillance programs.

Internet companies have vehemently denied initial news reports that said the government's Prism surveillance program gave authorities the ability to tap "directly" into the companies' networks or servers. But subsequent reports, mostly based on documents leaked by former NSA contractor Edward Snowden, have implied that intelligence agencies somehow get access to a wide range of Internet communications -- although those reports generally haven't specified how the information is obtained.

Those reports are "absolutely a concern" because they may lead to an erosion of trust in the Internet and in "the global credibility" of U.S.-based Internet companies, said Ed Black, CEO of the Computer and Communications Industry Association, a leading trade group.

Some foreign tech companies are already touting privacy and security features as an alternative to U.S.-based services, said Joseph Lorenzo Hall, a senior staff technologist at the nonprofit Center for Democracy and Technology. He added: "If U.S. products or services are seen to be fundamentally tainted, competent businesses will seek those services elsewhere."

The issue was compounded further last week by reports that the U.S. and British governments have waged an intensive campaign to crack Internet encryption methods used around the world. Reports by The New York Times and Guardian newspapers said those efforts involved a combination of cooperation, legal coercion and even secret hacking into the systems of unnamed tech companies.

That prompted more expressions of outrage by tech firms. "We are unaware of and do not participate in such an effort, and if it exists, it offers substantial potential for abuse," a Yahoo representative said.

A day later, the Washington Post reported that Google has expanded its encryption efforts by accelerating a program to begin encrypting all data as it travels between Google's server farms. Sources familiar with Google's effort said it's a year-old program intended to guard against rogue hackers and criminals as well as unauthorized incursions by any nation's government. Google, however, decided to speed up the system's implementation in June, after the company was rocked by the initial NSA leaks.

Facebook and other companies are also expanding their encryption efforts. Those systems can be a barrier to surveillance, analysts agree. But as Hall noted, the technology may not stop government data demands that come with the force of law.

Last week's reports, meanwhile, also described government efforts to exploit vulnerabilities or even build "back doors" in encryption chips, computer hardware and networking software from unnamed tech companies. Castro said that expands the field of companies whose products are potentially tainted by implication.

"So now it's not just Internet companies that have a target on their backs," he added.

Mercury News staff writer Steve Johnson contributed to this report. Contact Brandon Bailey at 408-920-5022; follow him at Twitter.com/BrandonBailey.