Just when you think there's nothing more you could possibly learn about the Vietnam War, along comes a book that offers a startling new glimpse at that monumental misadventure.

The new book is called "The Secret War Against Hanoi," and it describes for the first time some of the devious covert operations the United States ran against North Vietnam. I've been hearing bits and pieces of this tale from ex-spooks over the years, but seeing it gathered together by a careful historian, Richard H. Shultz Jr., is a revelation.

What you realize anew, reading this catalogue of spies and saboteurs and secret operations, is that Vietnam was a laboratory for the men who had fought and triumphed in World War II. They wanted to use the same clever tools of technology and deception that had confounded the Nazis. They had won the big war in 1945 partly through code-breaking and double-cross operations, and they couldn't imagine losing this little one in Asia. But they failed, and the reasons why are a telling restatement of the larger failure of Vietnam.

The secret warriors certainly fought as hard as our regular Army troops, and they came up with some monstrously clever ideas. But many of them were blunted by bureaucrats back in Washington, who had authorized the operations but weren't prepared to follow through on them. More important, our covert actions were confounded by a peasant enemy in Hanoi who was, in a sense, too primitive to appreciate the scope of our manipulations.

The secret war was launched in 1964, under the jurisdiction of the bland-sounding Military Assistance Command Vietnam Studies and Observation Group, known as MACVSOG. The heart of the program was psychological warfare, or "psywar," which was intended to confuse and demoralize the enemy.

Americans are good at thinking up nasty surprises, especially in wartime, and they came up with some doozies. They crafted fake Chinese ammunition that would blow up in the faces of North Vietnamese soldiers--making them mistrust their weapons. They put a contaminant in rice caches along the Ho Chi Minh trail that rendered the rice so disgusting even the maggots wouldn't touch it.

Some of the tricks were replays of techniques used in World War II. Our secret warriors sent fake letters with inflammatory information to unwitting recipients in North Vietnam, so Hanoi's secret police would think the recipients were traitors or spies. They created clandestine radio stations to broadcast propaganda. When this tactic seemed to be failing, because so few North Vietnamese had radios, they decided to ship in radios, too!

The jewel of the program--the black sapphire, if you will--was an effort to create a phony opposition movement in North Vietnam called the "Sacred Sword of the Patriots League." The name was meant to evoke the legend of the Vietnamese hero Le Loi, who had used a magical sword to expel the Chinese from Vietnam in the 15th century.

The imaginary opposition group began clandestine radio broadcasts in 1965, supposedly from its base in mountainous Ha Tinh province, which had been Le Loi's home base. Leaflets were dropped over the North Vietnamese countryside proclaiming its exploits.

To make Hanoi believe that a real resistance movement existed, the deception operation needed foot soldiers. They were gathered from among North Vietnamese POWs and poor fishermen who were kidnapped from the North Vietnamese coast by gunboats flying the Sacred Sword flag. From 1964 to '68, more than 1,000 of them were taken for "training" to a place called Paradise Island off the South Vietnamese coast, which had been fabricated to look like a liberated zone in the North.

Some of these Sacred Sword recruits were then parachuted into the North. Our dirty tricksters assumed most of them would be captured and tortured for information, but they didn't care. What they divulged about their training would only reinforce the myth that there was a real opposition group.

And our operatives were devilishly smart. They would parachute one Sacred Sword agent out the door first, and leave his comrades sitting on the bench--instead dropping a dozen dummy parachutes laden with blocks of ice. When the North Vietnamese found the empty parachutes on the ground, they would assume a far greater force had been sent in.

The poor Vietnamese agents would be given phony messages for other Sacred Sword units that didn't exist. Special spy gear and messages for this larger force would be sewn into their clothing.

It was a cynical exercise in a kind of covert tricks the British like to call "moving the furniture." And it seems to have played on the paranoia of the North Vietnamese, who came to believe that three times as many agents were operating in the North as was really the case.

But there was an inescapable problem. An imaginary movement to topple Hanoi's government could not be credible if it wasn't backed up in reality. And through all the machinations of MACVSOG, the politicians back in Washington refused to sanction any serious effort to overthrow the North Vietnamese regime. They thought that would be too dangerous.

In that sense, the United States was simply playing at dirty war in Vietnam. Operators in the field were encouraged to invent the sort of schemes that had been used so successfully in the ultimate war for life and death, World War II. But Vietnam proved to be an all-out struggle for only one side, and that was the side that ultimately prevailed.