Washington — To Gen. John W. Vessey Jr., US Army Vice-Chief of Staff, the Army's new M-1 tank is ''the best in the world.''
To others, the weapon - designed to defend against Soviet armor in Western Europe or the Middle East - isn't living up to expectations.
Tests of two tanks at Fort Hood, Texas, ealier this year indicate that steps to protect the crew from fire are inadequate. And congressional testimony and unclassified Army documents suggest that the tank's much-vaunted armor is more vulnerable that previously thought.
This newspaper has learned that high pressure hoses ruptured in a pair of test tanks at Fort Hood, sending hydraulic fluid squirting over the hot tank engines. The resulting fires severely damaged the two 60-ton behemoths, built by the Chyrsler Corporation. The Army says the resulting damage was ''fairly extensive.''
The Pentagon claims that the trouble-plagued tank uses a ''fire-resistant'' fluid in its hydraulic system, which raises and lowers its 105mm cannon and rotate its turret. But a source within the M-1 program stresses that use of the fluid renders the tank less than fire proof, and urges that a safer substitute be found.
An Army spokesman concedes that the fluid used in the M-1 is flammable but emphasizes that it is a lot less dangerous than the type previously employed in US tanks. ''It's the most fire resistant hydraulic fluid available,'' he asserts , noting that it was originally developed by the Air Force in its continuing effort to reduce the number of aircraft lost in combat to hydraulic fluid fires.
But M-1 critics contend that a safer hydraulic fluid could be found for the 7 ,058 M-1 tanks the Army wants to buy at a cost of $18 billion.
According to the Federal Aviation Administration, US civil aircraft use a hydraulic fluid called Skydrol, produced by the Monsanto chemical company. Monsanto spokesman Roger Hatton insists that Skydrol is more fire resistant than the hydraulic fluid currently used in the M-1. ''I believe it could have been put in the tank,'' he says.
Why is Skydrol not coursing through the hydraulic lines of the army's new tank? ''I'm not privy as to why the Army made the decision not to use it,' says Mr. Hatton.
The Air Force has no doubt that Skydrol is safer than the product now used in the M-1, which the Army has accorded the military specification H-83282.
According to a 1979 report published by the Aero Propulsion laboratory at Wright-Patterson Air Force Base, Ohio, Skydrol has to spill onto metal heated to 800 degrees C. before it will catch fire. By contrast, H-83282 fluid bursts into flames when it touches metal heated to only 325 degrees C.
An engineer interviewed by the Monitor contends the Army should use silicone hydraulic fluid in the M-1, claiming it is ''absolutely non-inflammable.'' Silicone fluid was approved for brake hydraulics by the Department of Transportation in 1974, says another source. But he notes that silicone fluid is heavier and more expensive than the hydraulic fluid currently used in the tank.
The fact that two M-1s suffered hydraulic fluid fires suggests to one Pentagon source familiar with US armor that the M-1's vaunted fire detection and suppression system ''maybe doesn't work.'' The system is supposed to smother fires in the tank's crew and engine compartments with halon gas.
But the Army's Materiel Analysis Activity at Aberdeen Proving Ground in Maryland compiled a report last summer that brands the system -- which is designed to activate in six milliseconds -- a ''critical hazard.''
Sensors in the tank designed to detect fires apparently aren't properly positioned. During recent testing it was discovered that these devices in the engine compartment could not be relied upon to detect all fires that might start there. In fact, the sensor in the driver's compartment would detect the muzzle flashes of the tank's main gun and discharge a blast of halon.
Hydraulic fluid fires in tanks are particularly lethal for crewmen. According to one former commander of an Israeli tank battalion, of 800 tankers killed in the 1973 Yom Kippur war, 300 deaths were attributable to hydraulic fluid fires. The Israeli Embassy in Washington, D.C., was unable to confirm such a toll.
Despite the fires in the tanks at Fort Hood and the problems with the M-1's fire extinguishing system, General Vessey claimed last month that the M-1's ''flame resistant hydraulic fluid and automatic fire detection and suppression [ system]'' give the tank's crew ''unprecedented protection.''
The M-1, whose cost has soared from $568,000 to almost $2.7 million (when research and development costs are included) each, continues to be plagued with what the Army freely refers to in private as ''design deficiencies.''
Documents obtained by the Monitor reveal that during cold weather tests, turret oscillation has on some occasions prevented the tank from firing its main gun. These same documents disclose that the tank is so noisy inside that crew members have difficulty communicating with each other and risk hearing loss.
''There is a high-pitched whine from the turbine engine,'' says a source familiar with the tank's interior. ''You have to scream to be heard over the intercom system.''
Sealing around the driver's hatch is apparently still inadequate, permitting snow, water, and cold air to enter the crew compartment. In desert testing, the M-1 exhibited low engine power and in frigid regions its air intakes ingested snow.
Testifying before the investigations subcommittee of the House Armed Services Committee Nov. 5, General Vessey conceded that the M-1 had not met requirements for its track life, the ratio of maintenance time to operating time, and the durability of its power train, made up of its engine, transmission, and final drive.
''We have not yet solved every M-1 problem,'' he said, ''but we have . . . shown that the M-1 is a very, very good tank.''
But the M-1 may not be as indestructible as the army likes to claim. Congressional testimony and unclassified army documents indicate that its Chobham armor is vulnerable to penetration by Soviet shells.
Some experts claim that although this revolutionary British armor provides good protection against high-explosive anti-tank rounds, it has no special capability against solid-shot, or kinetic energy, rounds that tanks use to destroy each other. The Army stoutly denies the claim.
One source says that it is because of the M-1's vulnerability to kinetic energy rounds, that the US Army Tank-Automotive Command in Warren, Mich., recently began soliciting bids for a turretless M-1 in which the commander and gunner would be housed in the hull and the main gun would be equipped with an automatic loading device.