When Congress and the executive branch collude to keep Americans in the dark about whether their privacy is being invaded, the Supreme Court should be willing to lift the veil of secrecy — at least to the extent of forcing the government to explain how often it is monitoring the confidential conversations of Americans.

The court abdicated that important watchdog role Tuesday when it ruled 5-4 that a group of journalists, lawyers and activists couldn’t challenge the constitutionality of a shadowy electronic surveillance program.

Tuesday’s decision came in a lawsuit filed by several people — including lawyers for suspected terrorists held at Guantanamo Bay — who claim that a 2008 law authorizing the surveillance of non-Americans abroad violates the constitutional rights of Americans whose phone conversations and e-mails might be caught up in the electronic dragnet.

That would be a challenging case to make, but the Supreme Court won’t even allow the plaintiffs to try. It dismissed their suit on the grounds that they lack “standing” to sue because they can’t prove that their conversations with sources and clients abroad actually have been monitored.

Writing for the court, Justice Samuel A. Alito Jr. said that the individuals who filed suit “merely speculate and make assumptions about whether their communications with their foreign contacts will be acquired” under the law. Alito was similarly scornful of the argument that they deserved standing because they had incurred expenses necessary to avoid being overheard and would have to travel to talk with clients face to face.

The requirement that individuals have “standing” — a concrete interest in a legal dispute — is an important principle. But, as Justice Stephen G. Breyer pointed out in his dissent, the court often has recognized standing in situations in which a possible adverse effect on a plaintiff wasn’t a matter of “absolute or literal certainty.”

Countering Alito’s strained analysis with common sense, Breyer argued that “we need only assume that the government is doing its job (to find out about, and combat, terrorism) in order to conclude that there is a high probability that the government will intercept at least some electronic communication to which at least some of the plaintiffs are parties.”

The law challenged in this case was extended for another five years by the last Congress, without amendments that would have required the government to provide an accounting of how often conversations and e-mail exchanges involving Americans were collected and accessed. The lawsuit blocked by the court on Tuesday would have provided another avenue for accountability.