The recent disclosure of U.S. surveillance methods is providing opponents of classified programs with new openings to challenge their constitutionality, according to civil libertarians and some legal experts.

At least five cases have been filed in federal courts since the government’s widespread collection of telephone and Internet records was revealed last month. The lawsuits primarily target a program that scoops up the telephone records of millions of Americans from U.S. telecommunications companies.

Such cases face formidable obstacles. The government tends to fiercely resist them on national security grounds, and the surveillance is so secret that it’s hard to prove who was targeted. Nearly all of the roughly 70 suits filed after the George W. Bush administration’s warrantless wiretapping was disclosed in 2005 have been dismissed.

But the legal landscape may be shifting, lawyers say, because the revelations by Edward Snowden, a former National Security Agency contractor and the principal source of the leaks, forced the government to acknowledge the programs and discuss them. That, they say, could help plaintiffs overcome government arguments that they lack the legal standing to sue or that cases should be thrown out because the programs are state secrets. A federal judge in California last week rejected the government’s argument that an earlier lawsuit over NSA surveillance should be dismissed on secrecy grounds.

“There is one critical difference from the Bush era. We now have indisputable physical evidence that the conduct being challenged is actually taking place,’’ said Stephen Vladeck, an expert on national security law at American University law school. He said Snowden’s disclosures make it “more likely” that cases will at least be allowed to go forward in court, leading to a years-long legal battle over surveillance and privacy.

A political debate over those issues has been roiling Washington since the British newspaper the Guardian reported on the telephone records program and published a classified court order to Verizon Business Network Services in which the NSA directed the company to turn over customers’ records. The information is “metadata” that includes the phone numbers dialed and the length of calls.

The Washington Post and the Guardian then disclosed the existence of a separate program, known as PRISM, that is aimed at collecting the online communications of foreign targets from major Internet companies.

Since then, three lawsuits have been filed challenging the constitutionality of the telephone records program: one by the American Civil Liberties Union in federal court in New York; another in federal court in Idaho by a nurse who is a Verizon Wireless customer; and the third in federal court in the District by Larry Klayman, founder of the conservative group Judicial Watch. Klayman also filed suit in D.C. federal court over the PRISM program.

Last week, the Electronic Privacy Information Center filed a petition with the Supreme Court asking it to vacate what it called the unlawful order to Verizon Business Network Services. “The records acquired by the NSA under this Order detail the daily activities, interactions, personal and business relationships, religious and political affiliations, and other intimate details of millions of Americans,’’ the petition said.

Legal experts said it would be highly unusual for the high court to get involved before other courts have considered the issue.

Experts said the cases challenging the phone records program have a better chance of success because so many people are Verizon customers and they could argue that their records were collected, and because officials have revealed more about it.

Some lawmakers also have argued that the phone records program is so broad that it exceeds the more targeted surveillance Congress envisioned when it reauthorized the USA Patriot Act provision, under which the program is operating.

The government has not yet responded to the cases, which are filed mostly against various government officials and argue that the programs violate the Constitution and invade Americans’ privacy. The ACLU suit, for example, asks that a federal judge order the programs halted and that the plaintiffs’ records be expunged from government databases.

A Justice Department spokeswoman declined to comment, but Obama administration officials have defended the surveillance programs as legal and necessary to protect Americans from terrorist attacks.

The Bush administration made similar arguments in support of its surveillance programs. Steven G. Bradbury, a Washington lawyer and senior Justice Department official in that administration, expressed skepticism that the new lawsuits would turn out better than previous ones.

He said the plaintiffs would have difficulty showing that they specifically were harmed by the programs, because the data collection was so vast, and that judges could rule that government officials are immune from such suits. And even though Obama administration officials have discussed the programs, Bradbury said the government could still get cases thrown out under what is known as the state secrets privilege.

Created in the 1950s and rarely used until after the attacks of Sept. 11, 2001, it allows officials to urge courts to dismiss cases on the grounds of potential damage to national security or foreign policy. “The further details of these programs are still state secrets,’’ Bradbury said.

Cindy Cohn, legal director at the Electronic Frontier Foundation, a digital rights group, said the state secrets argument doesn’t apply in cases involving electronic surveillance. She pointed to last week’s decision by a federal judge in California that rejected the government’s efforts to throw out on state secret grounds a 2008 lawsuit, brought by EFF, that includes earlier incarnations of the NSA’s surveillance programs, as well as current ones. The lawsuit is now proceeding.

Although other courts are not bound by the decision, Cohn said it could be a “tremendous boon” to plaintiffs in cases filed in the past month. “It’s tremendous, because anything that allows these cases to proceed is important,” she said.

She added that her organization plans to file a lawsuit this week stemming from Snowden’s recent revelations and that she has heard about at least two additional suits in the pipeline. Sen. Rand Paul (R-Ky.) also has vowed to bring legal action against the government over its broad surveillance efforts; a spokeswoman for Paul said he is evaluating his options.

Even if they wind up being thrown out, the lawsuits could still serve a larger purpose for opponents of the programs by raising public awareness of the issues surrounding surveillance and possibly forcing the government to make changes or disclose more. Other suits, legal experts said, helped force changes to the detention program at the U.S. detention facility at Guantanamo Bay, Cuba, and brought pressure on the administration to publicly acknowledge its campaign of drone strikes.

“There is a broader function to these lawsuits than simply winning in court,” said Jules Lobel, a University of Pittsburgh law professor who wrote a book about using lawsuits to achieve political aims. “The government has to respond, and forcing them to go before a court might make them want to change aspects of the programs.

“The government does things to avoid embarrassment,’’ he added, “and lawsuits are a key pressure point.’’