The United States has so improved its underwater detection systems that it may eventually be possible to destory the entire Soviet ballistic-missile-firing submarine fleet, according to a study by the Congressional Research Service of the Library of Congress.

The CRS study, based partly on classified and previously unpublished information, pointed to developing antisubmarine warfare (ASW) technology as one of several areas of strategic weapons development that are "unfettered by SALT" and "could prove profoundly destabilizing" in U.S.-Soviet relations.

The study noted ASW improvement had come "without... public awareness of the fact or its implications."

The study questioned whether advances in strategic ASW systems were consistent with U.S. arms control policy which is to encourage the Soviets to reduce their landbased ICBM forces in favor of submarines which are supposed to be invulnerable to attack. The theory is that if their subs are relatively invulnerable the Soviets will not press ahead as hard in other aspects of the arms race.

An administration official said yesterday the United States "has made very substantial progress on ASW" to the point where "it is no longer inconceivable that there might be a breakthrough," in U.S. ability to destroy the Soviet fleet.

Such a situation, the official said, is "of sufficient concern on our part because of what would happen if the Soviets were to achieve our capabilities." The thought is that, if we can do it to them, we should begin to worry that they can also do it to us.

He added that U.S. technological advances in ASW and the possibility they could be mirrored by the Soviets "had been one of the factors in the desire to maintain the land-based ICBM option." The Carter administration has been firm in its desire to preserve this alternative for the United States.

A second area of concern for future instability, the CRS study said, was "further advances in ICBM and SLBM [sub-launched missile] accuracy," by both the United States and the Soviet Union.

"Advanced inertial guidance systems that could be available in the late 1980s are likely to increase ICBM accuracy" to "a threshold where any reasonably sized warhead can destroy even a very hard target," like a missile silo, the study found.

To meet these technological advances, the study recommended "more stringent and qualitatively oriented constraints [be] implemented under future SALT stages."

The study's analysis of the U.S. ASW program brought out details on both the technical advances being achieved and what it termed the Soviet ballistic sub "vulnerabilities."

It disclosed, for example, that the Soviets already see a threat to their subs and have adopted "protective ASW" by accompanying their ballistic subs out of port with large numbers of their own ASW ships, aircaraft and attack subs.

In addition, the Soviets send only 15 percent or less of their ballistic subs out on patrol at any one time. In contrast, about 55 percent of the U.S. ballistic sub fleet is normally at sea.

According to the study, as of 1975, only three Soviet missile subs patrol in the Atlantic within range of the mainland United States and one in the Pacific.

Longer-range, newer Soviet missile subs, the study said, stay close to their home ports from which they still can hit U.S. mainland targets.

Even there, however, the study said the Soviet sub still could face a U.S. ASW threat. "Major assignments of the U.S. attack submarine force," the study said, "include not only barrier operations along the periphery" of the Soviet mainland, "but offensive operations in forward areas."

Sophisticated U.S. underwater listening systems are located in ocean areas surrounding the Soviet Union.

Application of computer technology to these systems has enabled "rapid overall increase in ASW effectiveness."

Supplementing the fixed systems are new generations of ship-towed listening devices, as well as aircraftdropped sonobuoys.

The technology is such that, according to sources, U.S. listeners can distinguish the peculiar sounds put out by each particular Soviet sub -- much like the voice of an individual. When that sub is at sea, computers can scan the recorded sounds and filter out its peculiar sound, thus helping keep track of it.

The U.S. system thus take advantage of a major weakness in the Soviet sub fleet -- the extensive amount of noise each sub generates.

Another weakness of the subs and the "Soviet navy in general," the study says, "is a dependence on a centralized satellite-based command, control and communications system."

In the event of a war, the study assumes, one of the first points of attack would be satellite systems used by both sides.

The study says and administration officials confirm that as of today the United States is far ahead of the Soviets in ASW.

The Soviets, according to the study, have "no effective capability for open-ocean ASW."

To illustrate the sophistication of the U.S. fleet, the study noted that "if detected by chance" a Poseidon sub "can launch from a torpedo tube a self-propelled acoustic decoy to facilitate evasion and escape." The decoy, sources said, sounds like the sub that it came from.

Administration officials yesterday were critical of any proposal to include ASW under the strategic arms limitation treaty (SALT).

They said that ASW is developed primarily for tactical reasons -- to protect the sea lanes for transport of troops and material by ships. Thus, they said, it is unlike anti-ballisticmissile systems that were traded away as part of SALT I.

"If we negotiate away our capabilities," one official said, "we would hurt our ability to defend supplies being sent to Europe."

Furthermore, he said, "we are far ahead and it is always difficult to give up in an area where we have an advantage."