As US lawmakers debate the legality of the National Security Agency (NSA) domestic surveillance project approved by President Bush, tech insiders are raising serious questions about the effectiveness of the program.

And attention is also being turned to which telecommunication companies have provided assistance to the NSA electronic surveillance effort, at the expense of customer privacy.

This comes amidst revelations by the Washington Times that Bush is spying on Americans talking to Americans inside the United States, even when neither of the two Americans are members of Al Qaeda or an affiliate. Attorney General Gonzales had previously told Congress - and President Bush has insisted for a month - that the only phone calls being tapped were ones where one party was abroad and one party was a member or agent of Al Qaeda.

Critics insist the President is violating the 1978 Foreign Intelligence Surveillance Act (FISA) which specifies when warrant-less intercepts of electronic conversations or data transfers are permitted. The Act created the secret Foreign Intelligence Surveillance Court, which approves requests for eavesdropping for national security reasons, and a Foreign Intelligence Appeals Court. President Bush has argued the FISA constraints are too restrictive, yet as Colonel Dan Smith writes in News World Communications, the latter has never heard a case, while the former has approved more than 18,745 applications.

Many if not most legal experts outside the administration reject presidential assertions that Congress allowed the snooping by giving him war powers, as stretching congressional intent. But the real issue may well be the effectiveness of the program. Critics claim Bush officials swept up so many messages - phone, mail and email - they simply didn't have the staff to sort through the messages to find the ones of significance. They ended up with millions of useless messages, and - since terrorists are presumably clever enough to talk in code - no ability to sort the wheat from the chaff.

The Washington Post reports intelligence officers who eavesdropped on thousands of Americans in overseas calls under authority from President Bush have dismissed nearly all of them as potential suspects after hearing nothing pertinent to a terrorist threat.

It says surveillance takes place in several stages, the earliest by machine. Computer-controlled systems collect and sift basic information about hundreds of thousands of faxes, e-mails and telephone calls into and out of the United States before selecting the ones for scrutiny by human eyes and ears.

Successive stages of filtering grow more intrusive as artificial intelligence systems rank voice and data traffic in order of likeliest interest to human analysts. But intelligence officers, who test the computer judgments by listening initially to brief fragments of conversation, "wash out" most of the leads within days or weeks.

It quotes national security lawyers, in and out of government, as saying the washout rate raised fresh doubts about the program's lawfulness under the Fourth Amendment, because a search cannot be judged "reasonable" if it is based on evidence that experience shows to be unreliable.

Meanwhile Declan McCullagh, moderator of the Politech mailing list, reports one unanswered question is which corporations cooperated with the spy agency.

McCullagh says some reports have identified executives at "major telecommunications companies" who chose to open their networks to the NSA. No company has chosen to make its cooperation public, presumably because they may have broken the law in divulging customer communications.

A survey by CNET News.com has identified 15 large telecom and Internet companies that are willing to say that they have not participated in the NSA surveillance program, as well as another 12 that declined to reply.