he veil of secrecy that still drapes much cold war history slipped briefly in 1967, when President Lyndon Johnson revealed one of America's worst-kept secrets to a Nashville audience: that the country had a reconnaissance satellite program. Estimating that the United States had by then spent $35 billion or $40 billion on space activities, Johnson said, ''If nothing else had come of it except the knowledge we've gained from space photography, it would be worth 10 times what the whole program has cost.'' Satellites routinely surveyed the Soviet Union, assuring American analysts that Soviet military assets were finite, known and at rest. This confidence allowed the two superpowers to survive the balance of terror without scaring each other into a war that neither dared to initiate.

''Secret Empire,'' by Philip Taubman, a longtime correspondent for The New York Times and now its deputy editorial page editor, chronicles the development of these ''national technical means,'' the euphemism for overhead reconnaissance, both aerial and space-based. Concentrating on the Eisenhower years, Taubman celebrates ''the inventors and risk-takers who revolutionized spying'' and calls for a new generation of technological swashbucklers to create tools for the perils facing the United States at the beginning of the 21st century.

It's a great story. Scientists and engineers convince President Dwight D. Eisenhower that strategic reconnaissance is necessary and possible. Kelly Johnson, the wizard of Lockheed Aircraft Company's legendary Skunk Works, designs and builds the U-2, an ungainly, fragile, greyhound of a plane with wings so long and flexible they need wheeled crutches to support them on takeoff. The Harvard optics expert James G. Baker devises a camera small and light enough to ride on the slim, featherweight plane but powerful enough to detect strategic weapons from 70,000 feet. A whole new office of photographic analysis has to be created to deal with the resulting data.

Dreading the consequences if the United States lost one of the planes, Eisenhower allowed only 24 flights in four years over the interior of the Soviet Union. By the time the U-2 pilot Francis Gary Powers crashed inside the Soviet Union in 1960, replacement programs were already at hand. The intelligence community had produced a satellite capable of legal overhead reconnaissance. Overcoming technical obstacles even more forbidding than those impeding aerial reconnaissance, the government lofted the Discoverer satellite in 1959. It began the technology extolled by Lyndon Johnson eight years later.

Overhead reconnaissance demonstrated that the so-called bomber gap of the mid-1950's and the missile gap of 1960 were political exaggerations. The United States moved through the cold war with more confidence and less escalation of weaponry than would have been possible without the assurances provided by the U-2's and spy satellites.

Taubman tells this story with effervescent admiration for the heroic inventors and a fine eye for revealing anecdotes. For example, Edwin Land, the inventor of the Polaroid camera and confidant of Eisenhower, believed in small, no-nonsense meetings; an automobile provided about the right amount of space. When he sought to convince his colleagues of the feasibility of the U-2 design, he invited the Cornell aerodynamicist Allen Donovan to a meeting in Washington. When Donovan arrived, Land met him in a Ford sedan driven by the Princeton mathematician John W. Tukey. Also in the car were the camera designer Baker, the Harvard Nobel laureate in physics Edward Purcell and James B. Fisk, later to become president of Bell Labs. Tukey drove the six of them around Washington for two hours while Donovan expounded on the virtues of the new airplane.

Most of the material in ''Secret Empire'' has already found its way into the public realm. Students of cold war espionage, like James Bamford, William E. Burrows, Curtis Peebles and Jeffrey T. Richelson, all of whom Taubman acknowledges, have been chipping away at the wall of government secrecy for decades. Their work has been complemented in recent years by the government itself, which has released previously classified C.I.A. records and internal histories. Taubman's contribution is to combine the earlier material with the most recent revelations into a lively and engaging story.

For all that it reveals, however, ''Secret Empire'' demonstrates that layers of secrecy still stand between the American public and a full understanding of the cold war. Taubman relies, perhaps overmuch, on memoirs and interviews, for the simple reason that he was denied access to much of the documentary record. He notes that most of the activity he chronicles was on the government's notorious ''black budget'' -- the U-2 flew for a year before any member of Congress knew of its existence -- and he offers little hard evidence to back up President Johnson's claims about costs and benefits. He reports some of the bureaucratic battles between the Air Force, the C.I.A. and the National Reconnaissance Office, but he can't begin to explain the byzantine history behind current attempts to restructure the American intelligence community. And he provides a tantalizing but necessarily incomplete hint of the human toll of cold war reconnaissance, the hundreds of air crewmen lost on spy flights over the Soviet Union and other countries of the Communist bloc.

In the end, Taubman suggests that the intelligence revolution of the 1950's may have been too successful. The United States, he believes, has become too reliant on overhead reconnaissance. Humint (human intelligence, that is, spies) has been allowed to atrophy, much as high-risk missions by American servicemen and women are being taken over by standoff weapons and drones. For all its powers, overhead intelligence cannot reveal many things the nation needs to know, especially now, since the war on terrorism requires intelligence of a very different sort. Taubman's call for a new wave of heroic innovation plays down the particular circumstances described so colorfully in his book. The technologies of overhead reconnaissance were young and ripe in the 50's, the target was huge and accessible, the scientific and technical communities were mobilized and empowered, and the government moved with daring and dispatch. It is not clear that this history can or will repeat itself.