The U.S. Navy submarine was slipping through the waters off the Soviet coast, its skipper confident he would hear the Russian sub he was hunting before its captain heard him.

With a loud metallic ping, the Soviet sub hit the American boat with a sound wave. The Soviet skipper had heard his pursuer before he was detected by the U.S. vessel's listening gear. Safely hidden, he had "challenged" the American hunter by sending a sound wave against his hull. In that instant, the American hunter became the hunted.

The incident last year, according to U.S. officials, was one of several that shook up Navy leaders. Another shock came when a U.S. attack sub followed a characteristically noisy Soviet sub to the entrance of its home port. A few months later the Soviet sub returned to the open sea quietly, thanks to the installation of a new propeller.

These disturbing events from the shadowy world of underwater eavesdropping accelerated the Reagan administration's hunt for foreign companies that had sold the Soviet Union the machinery needed to make such propellers. Firms in Japan and Norway eventually were fingered as the culprits, straining relations with the United States. Congress has reacted bitterly, moving to ban foreign companies responsible for the security breach from selling products in the United States.

The longer-term consequence of quieter Soviet submarines is a shift in the U.S.-Soviet balance of power under the sea. How big a shift is now in dispute. But there is no dispute that Soviet subs have become significantly quieter, posing an unwanted new challenge to the Defense Department.

Quietness can be a matter of life or death in undersea warfare. The submarine skipper who hears his enemy first can fire first and live. His torpedo rips open the other sub. Because the United States and the Soviet Union carry hundreds of nuclear warheads in intercontinental ballistic missiles aboard many of their submarines, quietness enters the doomsday calculus of which superpower would "win" -- if there were a winner -- a nuclear war.

The Soviets' sudden closing of the noise gap has put the U.S. submarine community on the defensive for the first time since the submarine USS Nautilus made history in 1955 by getting under way on nuclear power. Former Navy secretary John F. Lehman Jr. and admiral James D. Watkins, recently retired chief of naval operations and a submariner, have blamed the spy ring headed by former Navy radioman John A. Walker Jr. for the sudden Soviet advances. Defense Secretary Caspar W. Weinberger and other administration officials are blaming Japan and Norway for allowing their high-tech companies to ship to the Soviet Union the technology needed to manufacture smooth, quiet submarine propellers.

But those explanations are only the latest chapters of a long book, according to antisubmarine warfare (ASW) specialists inside and outside the government. "Quieting submarines is a laborious process of doing a lot of little things," one veteran ASW specialist said.

The Soviets have been doing that at the same time that they dared to go beyond the technologies pushed by the late admiral Hyman G. Rickover, the dictator of U.S. submarine design for three decades, the specialist said. As a result, he said, in addition to better propellers, Soviet boats today incorporate advances in power plants, metallurgy, hull shapes, low-friction coatings and a broad range of quieting techniques.

"The stuff the Soviets got from Toshiba and Kongsberg helped them manufacture smooth, precisely shaped propeller blades," said another ASW specialist and former Navy submariner. "But somebody had to design those propellers and do the engineering . . . the real breakthroughs the Soviets made to make their propellers quiet, not the milling by Toshiba's machines."

Starting in 1982, the Toshiba Corp. of Japan falsified records, according to the Japanese government, to enable it obtain the export licenses to send milling machines to the Soviet Union. In 1983, Kongsberg Vaapenfabrik of Norway began shipping computer controls for the four Japanese milling machines, according to U.S. officials. They added that Norwegian employes of Kongsberg went to the Soviet Union in 1984 to tune up the computerized machines. Administration officials said a Toshiba employe tipped off the U.S. government to his company's deal with the Soviet Union.

"We were told to listen for different signatures on Soviet submarines," said one Pentagon official, reconstructing the detective story that reached under the sea. "The evidence began piling up last year."

Although he did not disclose how the undersea evidence was gathered, it is an open secret that U.S. and Soviet attack subs play a constant game of hide-and-seek in the depths, recording the noise emitted by each other's propellers, machinery and hull.

Also, most of the friendly coasts of the world have submarine-listening devices installed on the sea bottom, officials said. The distinctive "signatures" -- the noise a Soviet submarine makes as it moves through the water -- are kept on file, like fingerprints, by the National Security Agency. U.S. skippers use this data to identify Soviet quarry. The Soviets employ a similar system to identify U.S. subs.

Armed with evidence gathered by underwater eavesdropping, Fred C. Ikle, undersecretary of defense for policy, went to Tokyo last winter to complain about Toshiba's security breach. Complaints by Ikle, Weinberger and other administration officials prompted the Japanese and Norwegian governments to investigate the high-tech shipments and take punitive actions against the executives involved. The Senate and House are attempting to add to that penalty by banning, with some exceptions, shipments of Toshiba and Kongsberg products to the United States.

Although some administration officials said the firms' big assist to the Soviets' submarine-quieting will cost the United States up to $20 billion to overcome, Ikle said in an interview that an accurate estimate cannot be made because no one knows how soon the Soviets would have quieted their submarines without the gear supplied by Toshiba and Kongsberg. However, he said the breach is "very serious" and probably will cost "billions" to correct.

Vice Adm. Bruce DeMars, deputy chief of naval operations for submarine warfare, said Soviet advances in quieting should be attributed to more than just new propellers.

"Their recent perceived gains are more evolutionary than revolutionary," he said on a recent "MacNeil/Lehrer NewsHour."

"What it means in the aggregate is that they have closed a little bit of the margin of submarine superiority that we hold over the Soviet submarine forces."

Navy Secretary James H. Webb Jr., a former Marine Corps officer who took a skeptical look around right after taking office in April, has been convinced by Adm. Carlisle A.H. Trost, chief of naval operations, DeMars and other submarine leaders that there is nothing wrong with the undersea balance that construction of the new Seawolf (SSN21) class of submarines cannot fix.

Webb termed the Seawolf "the true supersub of the 1990s" in a letter that sought to assure Chairman Charles E. Bennett (D-Fla.) of the House Armed Services seapower subcommittee that the Seawolf would be worth the $1.7 billion the first one will cost. "It employs the very best technology and will counter the best Soviet submarine well into the 21st century." Bennett and other subcommittee members later overturned their research subcommittee's finding that the Seawolf would not be good enough to combat the Soviet undersea threat of the next century.

Anthony R. Battista, the House Armed Services Committee's research specialist, is a vigorous critic of the SSN21 Seawolf. He argued -- successfully for a while -- that Congress should force the Navy to design a better submarine than the SSN21 and rely on improved versions of the SSN688 Los Angeles-class attack boat in the meantime. Norman Polmar, a specialist who has been a Navy consultant in the past, is among Battista's allies in the Seawolf fight.

Although the Seawolf, scheduled to go to sea in 1994, is back on course in Congress, its long-range future has been clouded by Soviet advances on its own Akula (Shark) attack boats and other subs and Pentagon money shortages ahead as Congress flattens the defense buildup with less sharply rising budgets.

Submarine specialists inside and outside the government said these developments have forced these questions on the administration and Congress as it decides how a limited amount of defense money should be apportioned in the years ahead: Since it will take more attack submarines to find the quieter Soviet submarines, how will the Navy get the money needed to expand its fleet above the current goal of 100 nuclear-powered boats? By the year 2000, only six years after the first Seawolf goes into service, the Navy will be faced with "block obsolescence" as most of the Sturgeon- and Permit-class attack boats now operating reach or exceed the usual service life of 30 years.

The Navy will have fewer attack subs in the 1990s than the 97 it has today because of the budget crunch and the wearing out of dozens of boats at once, one Pentagon executive has concluded. "The Russians have only a few of these new, quiet Akula-class attack subs out there," said the official, who declined to be quoted by name, "so we have time to rethink whether we can afford to buy enough SSN21s." Is it time to switch detection techniques from silent, passive eavesdropping to active "pinging," or sound-wave propagation under the waves, because U.S. and Soviet submarines will soon be too quiet to detect at long ranges by today's techniques?

A member of the Joint Chiefs of Staff said this question was being studied by the Navy but not yet by the staff of the chiefs. The prevailing attitude among submariners is that eavesdropping, rather than pinging, is still the way to go. But some specialists contend it is time to take a fresh look at active detection, such as an old Navy program called Project Artemis, named after the Greek goddess of the hunt.

Under Artemis, the Navy in 1961 experimented with sending sound waves through the sea to detect submarines. One idea was to scatter barges carrying sound makers around the world's oceans. The sound wave would bounce off a submarine and be picked up by underwater microphones on the ocean floor, enabling operators on the barge or on shore to triangulate the sound and pinpoint the submarine.

Robert A. Frosch, director of General Motors Research Laboratories, directed Artemis in the 1960s as deputy director of the Pentagon's Advanced Research Projects Agency (ARPA). He recalled in an interview that active detection development was abandoned in favor of passive detection systems because "the Soviets subs were noisy, ours were quiet, so what the hell?"

While Artemis is back on the table, submariners caution that if barges or hunter submarines send out searching sound waves, rather than listen, they give away their presence and position to the enemy. Has the Navy's proclaimed "forward strategy" of rushing attack subs into the Norwegian Sea to bottle up or sink Soviet missile submarines been made obsolete by the new parity in submarine silence?

Adm. William J. Crowe Jr., chairman of the Joint Chiefs of Staff and a former submariner, has never been enamored of the forward strategy espoused by Lehman and Watkins. Crowe calls it a concept, not a strategy, which theater commanders may choose to ignore in times of tension or war. Other Defense Department officials said the forward strategy started to sink as soon as Lehman left the Pentagon in May. If U.S. and Soviet subs have to get dangerously close to hear each other, bayonet-close, so to speak, is it time to abandon the strategy of sending one submarine to kill another and restrict the mission of attack submarines to bombarding shore targets with cruise missiles and laying mines?

One former submariner, who asked that his name be withheld, said that day has arrived, even though Navy leaders do not realize it. He added that the U.S. attack subs' long-range torpedo, the Mark 48, which sends out sound waves to find its targets, is unsuitable for the close quarter duels being forced on the two superpowers' undersea forces by parity in quietness. Under such conditions, the Mark 48 could turn around and sink the sub that launched it, said the former submariner, despite safeguards designed to prevent this.

"Using the submarine for antisubmarine warfare is no longer interesting," he said.

Today's submariners dispute that claim. "Our submarine force could clean up on their navy if we went to war today," DeMars said.