DO YOU WANNA know a secret? If so, there's no need to go out and find yourself a Deep Throat. All you need to do is to visit a good library.

The U.S. government runs some of the best. It was in government libraries that a writer for The Progressive magazine (in an incident now long forgotten) found official papers which helped explain the technology required to make a nuclear bomb.

Even if you have no ambition to blow up the world, the kinds of secrets you can find in libraries are quite amazing. At many neighborhood libraries, you can read defense magazines like Aviation Week and Space Technology and Electronic Warfare which publish detailed information on such frivolous topics as American intelligence about Russian missile tests and the latest innovations in U.S. military aircraft design.

A reader of Aviation Week would have learned in l978 that the U.S. Defense and Energy Departments had set up a committee to study whether to build radar spy satellites. With such satellites U.S. intelligence could see Russian missiles, planes and ships through heavy cloud cover. Apart from his disclosure that the Pentagon eventually gave this project cute codenames like "Indigo" and "Lacrosse", Bob Woodward, in his new book "Veil," tells aerospace magazine devotees little they didn't already know about this whiz-bang scheme.

Telephone books are another juicy source of defense and intelligence secrets. The Pentagon phone book, which can be perused at a good government library (or purchased for $9 from the Government Printing Office) is a treasure trove. Its Yellow Pages offer not only inquiring journalists but also the most nearsighted foreign agents an up-to-date account of the organization and key personnel of critical defence and intelligence offices, suchas the Defense Intelligence Agency and the National Military Command Center. They also offer an up-to-date listing of most current Army, Navy and Air Force weapons projects and their managers (to find Stealth, you might have to read between the lines).

James Bamford, author of "The Puzzle Palace," says the Pentagon phone book helped him unravel the mysteries of the U.S. government's most secret outfit, the National Security Agency (whose employees joke that its initials stand for "Never Say Anything" or "No Such Agency".) Bamford used the section in the front of the book which lists the military communications system phone numbers for installations around the world to locate secret NSA listening posts.

Excessive interest in telephone books can get you into big trouble in some countries, if not the United States. Ten years ago, while I was working for a London newspaper, the British government decided to expel me from the country for having "obtained for publication information harmful to . . . national security".

British authorities never said exactly what it was I obtained, but they invited me to explain to a secret tribunal of three "wise men" why I should not be expelled. I was unsure exactly what they wanted me to explain until they started vigorously cross-examining a colleague I had called as a supporting witness about a story we had co-written for a London magazine on the subject of Government Communications Headquarters, the British equivalent of America's NSA.

This was an agency about which few articles had previously been published and the "wise men" were curious about where we got our inside dope. We pointed out that virtually all of our information came from publicly available material, such as defense contractors' promotional brochures and obscure local newspapers. But the inquisitors were unconvinced. They were particularly annoyed that my colleague had compiled a map of secret GCHQ listening posts scattered around the British Isles. The wise men seemed to find it hard to believe my co-author when he said that all the information had come from local phone books -- even though he was telling the truth.

The fact that real secrets, like plans for new spy satellites and the names of secret agents, can be discovered from commonplace sources is one important reason why the U.S. government finds it difficult to control news leaks and investigative reporters. Moreover, in a democratic society, even draconian censorship powers do not necessarily help governments keep secrets.

By using archaic secrecy laws to ban "Spycatcher," the memoir of former counterintelligence officer Peter Wright, for example, Britain has recently succeeded in turning a dubious and malicious volume into an international bestseller. By cracking down on journalists who read telephone books, recent British governments also have fostered a whole new genre of paranoid literature in which its intelligence agents are the villains rather than the heroes: in two recent films, ("Defense of the Realm" and "The Whistleblower"), the government disposes of annoying reporters by killing them. Fortunately, there is no evidence that real-life British intelligence agencies use such drastic methods on journalists.

Given the enormous moral disequilibrium between democratic and totalitarian societies when it comes to the availability of government information, many journalists who poke around the world of secret government activities do recognize that not all secrets that can be found should be published. Some of us learn this point the hard way.

But if the government feels strongly that dangerous boundaries are being crossed, it might do better to draw clear lines before cracking down: The law prohibiting the publication of intelligence agents' identities has quite effectively (and properly) dampened a mischievious practice without really trampling on civil liberties. For in the long run, a free flow of information lubricates our democratic system, much as the absence of information fossilizes totalitarian society.

Mark Hosenball is a Washington-based correspondent for The Sunday Times of London.