In 1962, when the U.S. Army hired a civilian contractor to maintain its combat radio network in South Vietnam, the Army cheerfully guaranteed that its 39th Signal Battalion would be ready to shoulder the duties by September 1963.

"But the civilians were still there until the bitter end 13 years later in 1975," said John D. Bergen, a recently retired Army signal officer who also served as chief speech writer for Defense Secretary Caspar W. Weinberger.

The Army ordeal in building and sustaining a war-zone radio system foreshadowed nettlesome issues the Pentagon faces today as it ponders the care and feeding of complex weapons.

Throughout the U.S. war machine in South Vietnam, the contractor crutch was critical.

At one point, 2,000 industry technicians helped keep the Army's helicopters hovering, according to the Army's aviation logistics office.

Although most contractors displayed courage if exposed to fire, they enjoyed an umbrella of U.S. air superiority because the enemy had no air force.

This usually prevented attacks on depots, a luxury few experts anticipate in another large war.

In a forthcoming book about Army communications in Vietnam, Bergen documents how combat can stress logistics, even for relatively simple equipment. Examples include:

* When the Army wanted a new lightweight FM radio, a model called the GRC163 was developed in only 12 months and sent to troops during the Tet offensive in early 1968. Within months, the radios began to break down because "in the haste of putting the equipment in the field, the Electronics Command had been unable to prepare and distribute technical manuals and parts lists."

* The Army also had an unhappy experience with batteries for a small squad radio. Heat and humidity turned them "into masses of dripping cardboard."

* Broken radios were shipped from Vietnam to California in special packages called "jiffy bags." By 1969, repairmen were swamped by the 5,000 radios arriving every month. Army signal units grew so desperate for spare parts that they designated official scavengers, known as "scroungers," to snatch supplies before they were lost in cavernous military warehouses.

* After finding that Thai militiamen were inept at using FM radios, the Army hired several linguists to determine whether "the tonal qualities of the Oriental voice were not capable of transmission over FM radio frequencies."

After a year of study, the scientists concluded that the Thais were simply confused by the radios, "which appeared to uneducated militiamen as a strange, unintelligible combination of dials and buttons."