THERE ARE AT LEAST 50 million classified documents maintained by the United States government at a cost of some $300 million a year. They are stored behind an array of locks, dials, buzzers and single-minded security Myrmidons that would make James Bond cringe. One such document lay like a time-bomb in the FBI file of James Baldwin, writer.

To protect it from all but the most authorized eyes, it bore these prohibitions: "SECRET - NO FOREIGN DISSEMINATION (twice); GROUP I excluded from automatic downgrading and declassification: Not to be distributed outside your agency; Racial matter."

Even its collecting agency was classified. It came, said the document, from NYT-1, presumably the CIA but identified only as a U.S. intelligence agency operating in Turkey. But for all that, its contents proved less than intelligence dynamite:

"Baldwin's method of working is strange," it said disappointingly. "There are times when he writes continuously for 24 hours without food and drink. Under such circumstances, he does not even notice if you shout at him or hit him on the shoulder. Afterwards, he lies down and sleeps . . . If you are able to awaken him, how fortunate you are."

That is the horrible truth. Baldwin works 24 hours and thereafter needs sleep. And other secrets, too, are revealed in the three-page document: that Baldwin is black and writes about blacks; a list of his books; that he likes Turkey.

Where did this "secret" originate? Look, stock and barrel from a Turkish newspaper, the Milliyet. Our taxes paid for it to be retyped, for its guards, its storage, its indexing, and to devise an even costlier system to make sure no more news clips leaked out of the security sanctums.

The vast majority, perhaps 98 per cent of all classified documents, have no more business being classified than the Baldwin news clip. Yet they are, and this is the topic addressed with efficiency and irrefutable constitutionalism by Morton Halperin and Daniel Hoffman in Top Secret.

Their concern, of course, is not such mindless overclassification of trivia about writers from newspapers clips even considering the waste of money. What they stress is that keeping information from the public actually abcesses the heart and the brain of democracy.

The 17,000 rubber-stamp wielding censors, in the most realistic terms, permit wars to begin without Congressional or public assent. They permit world figures to be blackmailed and killed by U.S. agents, or with U.S. connivance. They permit trackless billions to be siphoned off by crooked contractors and officials.

Halpherin, an engaging and incisive former aide to Henry Kissinger and once a Pentagon bigshot, was a victim of Nixon era wirelapping. He should be the perfect Coeur de Lion for the crusade against suppression of information.

But alas, he has written a book so dull that it makes Das Kapital seem like Washington: Behind Closed Doors. Top Secret is about as stimulating as a topectomy, and the book's juicelessness is a major flaw.

To make a case that excess secrecy will strangle democracy, there should be some evidence of democracy strangling, gasping for air. Top Secret warns of democracy's death, but we don't see her dying. There is nothing to make us want to drop everything, to risk all to save her, as the authors want us to do.

In writing about the secret bombing of Cambodia, for example, where are the explosions of blood, bone and sinew, of honor, of cash that the secrecy occasioned? Where is the outrage that none of our leaders or military brass were prosecuted for their lying? Where is the why, the systolic-Diastolic why ?

Void of passion, yet in a passionate cause, Top Secret is a lawyer's brief, and yet its terrific value overshadows its infuriating disappointments.

Thoroughly footnoted, generously citing books of related interest and wider appeal, superbly organized. Top Secret does show us the essential way out. Almost as if writing legislation, Hoffman and Halperin explain how Congress can take over the monitoring of secrets and bring government a giant step closer to the people.

They recommend an independent screening board, repeal of some laws and rules that encourage overclassifying, a fair shake for whistleblowers, or at least equal punishment for those who overclassify.

Preeminently, they tell us - starkly - that letting the people know what is going on in all but the most limited, justifiably secret areas is worth the risk of opening up the files. Not to do so, they say, is disaster.

In sum, they propose an old, radical thesis; that governments are instituted among men, deriving their just powers from the consent of the governed.