The Pentagon is spending tens of billions of dollars a year on airplanes, ships and missiles that depend too much on radar, making the Air Force, Navy and Army vulnerable to enemy weapons that detect and home on radar signals, according to an article in a leading engineering journal.

Although it has been known for years that a radar signal can be a beacon for enemy sensors, the United States has neglected development of less vulnerable radars and countermeasures, said Thomas S. Amlie, a longtime missile designer and former technical director of the Naval Weapons Laboratory.

The headline on the article, published by the Institute of Electrical and Electronic Engineers in the April issue of Spectrum, states the question: "Military Radar: Shield or Target?" The subheadline reads: "Costly radar being developed by the U.S. may give an opponent a decisive advantage by broadcasting the position and makeup of forces."

Amlie wrote: "No sane infantryman engaged in heavy combat would run to the top of a nearby hill, light a flare, and dare the enemy to hit him. Yet some $50 billion a year . . . goes to develop, buy, and support radar systems that do the electronic equivalent of exactly that. For 20 years, many in the U.S. defense establishment have been aware of this problem but have swept it under the rug."

He said some of the most advanced and expensive weapons are the most susceptible to enemy missiles that home on radar signals, including top-of-the-line aircraft such as the F14, F15, F16 and F18 fighter bombers, the planned B1 bomber, and Airborne Warning and Control System planes. His list of highly vulnerable weapons includes the Navy's Aegis cruiser and the Army's Patriot ground-based air defense missile.

The Soviets have some air-to-surface missiles that home in on radar signals, but it is uncertain whether they have developed air-to-air or surface-to-air versions.

Robert D. Turner, an assistant deputy undersecretary of defense, said that the Pentagon is well aware of the problem and is making efforts to protect the U.S. forces that rely heavily on radar.

"There are no simple solutions," he said. "You're sort of stuck with radar."

Turner said there are conditions in which the military must shut down radars or use them in ways intended to deceive a possible enemy. In a lengthy interview, he discussed but did not dispute some of Amlie's key points, and he offered no direct denial of the central thesis that Amlie put this way: "The radar-dependent systems being developed and deployed by the U.S. give an opponent a decisive advantage by broadcasting the position and makeup of military forces to anyone who chooses to tune in."

Robert Bernhard, an editor of Spectrum, said the article had been given a pre-publication "peer review" by four experts, including two he described as "the biggest muckety-mucks in the radar industry."

Thomas D. Davies, a retired rear admiral who headed Navy research and development and who is a former assistant director of the Arms Control and Disarmament Agency, said in a recent interview that he generally agrees with Amlie's charges that the United States has not done enough to protect its forces from enemy missiles that home on radar signals, which are known as anti-radiation missiles or ARMs.

"The Pentatgon bureaucracy, with a few notable exceptions, hasn't tried to do anything to improve the situation," he said. Once, when he commanded a carrier task force, Davies said, he modified an existing radar to deceive the enemy, only to find the project abandoned after he was reassigned.

An expert on naval weaponry, asking not to be named, said in an interview:

"The Navy has what it calls 'emission control,' in which the ships turn off their radars. But in doing that, it turns out, the ships become totally unsuitable for the task at hand, because, once the radar is turned off all they can do is listen with 'passive receivers' for enemy signals and sparsely use the radars in very short bursts. The passive receivers are hopelessly inadequate . . . . And turning the radars on and off for short periods greatly increases their failure rate, because they were not designed to be used that way. That's the heart of the problem.

"Instead of designing the ships to work as well as possible in the 'radio silence mode' that they will have to use all the time in real war, they designed them -- at far greater expense -- to operate in a continuously emitting radar mode that can be used only in peacetime."

Amlie said the Navy perhaps has the greatest vulnerability. "The Navy has an almost insoluble problem, because ships are excellent radar targets and ships' radars are even better targets," he wrote.

In general, however, Amlie emphasized in Spectrum, "The solution is not to eliminate radar, but rather to design new radar systems" that reduce "their vulnerability as targets." Such systems could be used "in brief bursts" or operate on low frequencies, requiring impractically large antennae on enemy missiles that seek and home on radar radiation.

"Properly used, radar can give U.S. military forces a decisive advantage by locating enemy missiles, aircraft, warships, and battlefield weapons without giving away the radar's position," he said in an interview.

Amlie also said missiles that home on radar signals "are by far the simplest and cheapest guided missiles to build." In Vietnam, the United States used a Navy air-to-air missile named Shrike that homes on radar radiation. "It did indeed work -- but not always as intended," Amlie wrote in the article.

"U.S. Shrike missiles hit U.S. Marine units that had not shut down their radars. Similarly a Shrike accidentally attacked the U.S. destroyer Worden in the Gulf of Tonkin; it homed in on the ship's radar, exploded 100 feet directly over the superstructure, and disabled the ship's command center."

Production of Shrikes was stopped but some remain in inventory, Amlie said.

Amlie's "most extreme example" of possibly "self-defeating" radar-dependent weapons is the Aegis cruiser, which has the primary purpose of protecting a carrier task force against air attack. The ship is fitted with an array of radar "so elegant that it can be accurately said to have 16,400 little radars on it," he said. It requires the addition of 450 tons to the ship's displacement and increases its cost from about $400 million to about $1.3 billion.

"The radar transmits very strong signals different from those of any other radar in the world, making it a superb target for anti-radiation missiles that could be launched by an airplane, a ship over the horizon, or a land installation," Amlie said.

Amlie also cited Patriot, which is intended to protect troops from aerial attack. "Just like the Aegis, it transmits very strong and distinctive signals, and would be very easy to destroy with a simple missile," he said.

Turning to the Navy F14 and Air Force F15 fighter bombers, Amlie said the major reason they cost $30 million to $40 million each is that they are built around expensive and sophisticated radar. An enemy armed with missiles that home on this radar's signals could inflict "appalling losses" unless the U.S. pilots turned their sets off, he said.