In East Germany, they are everywhere -- and nowhere.

The 380,000 Soviet troops based in East Germany form the highest concentration of foreign soldiers in any European country. Posted on the front line of the East-West divide, they serve in the vanguard of Moscow's extension of military power, as well as offer insurance for the political legitimacy of local communist authorities.

Yet "the Guards of the Regiment," as Soviet troops in Eastern Bloc states collectively are known, generally are regarded by allies as an unloved occupation force rather than brothers in arms. They are held in scarcely concealed contempt by many East Germans, but discussion of their presence remains an alarming taboo.

They are rarely seen in public, but occasionally, clusters of Soviet soldiers, conspicuous in their brown uniforms and with Slavic or Asian faces, venture out to visit war memorials. Fraternization with the local population, however, is scrupulously avoided.

"The typical Soviet soldier in East Germany lives as if he were in a cage," said Harald Rueddenklau, a Soviet military authority at the German Society for Foreign Policy, a leading West German think tank. "He makes no contact with the East German population, nor do the Germans want any."

In terms of the military calculus of East-West relations, the 20 Soviet divisions in East Germany also present one of the more critical yet enigmatic factors in the amorphous equation known as the European balance of power.

The "Group of Soviet Forces in Germany," their official title, form the Soviet Union's largest and best equipped military contingent abroad. The troops in East Germany supposedly are better educated than most Soviet soldiers, and they are armed with the latest models of tanks, fighter-bombers and helicopters in the Soviet arsenal, according to western intelligence sources and other experts.

In a purported good-will gesture five years ago, Soviet ground forces in East Germany were cut by up to 20,000 troops and 1,000 tanks following a speech by then-Soviet leader Leonid Brezhnev marking the 30th anniversary of the German Democratic Republic.

Western intelligence officials said the move was largely cosmetic, because the quantities of troops and weaponry deployed by the Soviets in East Germany still exceed the combined forces of Britain, France and the United States in West Germany.

Despite the sensitive nature of Soviet forces in East Germany, the three western allies have been able to conduct daily patrols, tantamount to legally sanctioned espionage, by their 14-member military liaison missions based in Potsdam, outside East Berlin.

Under 1947 accords regulating occupied Germany, the Soviet Union is allowed to maintain three similar missions accredited to the former American, French and British sectors in what is now West Germany.

As they roam across the German countryside in cars crammed with sophisticated listening devices and infrared cameras, the liaison teams are said to accumulate what is considered the best on-site intelligence available in Central Europe.

The Soviet and western commands declare some areas off-limits to the liaison missions, and last year the commander of Soviet forces in Germany, Gen. Mikhail Zaitsev, expanded the size of forbidden territory to include 40 percent of East Germany.

Such restrictions are not necessarily obeyed, and both Soviet and western units are known to bend the rules to get a closer look at maneuvers, missile sites or ultramodern weaponry.

In March, Maj. Arthur D. Nicholson Jr., 37, a Russian-speaking member of the U.S. liaison team, was shot and killed by a Soviet sentry while photographing Soviet military equipment through the window of a shed near Ludwigslust.

U.S. officials contend that Nicholson was at least 300 yards away from a restricted zone, but the Soviet Union insists that he was within a forbidden zone and that the sentry who shot him followed acceptable procedures.

Despite the uproar that ensued over the conflicting versions of the killing, both U.S. and Soviet military commanders have made known their desire to prevent the incident from jeopardizing the fate of the liaison missions, whose espionage work offers unique early-warning notice of unusual troop movements that would otherwise trigger alarm about an imminent invasion.

The liaison units, by listening in on radio communications, counting and photographing tanks and aircraft and monitoring troop movements, have been able to glean highly detailed information on the capabilities and firepower of the Soviet forces in East Germany.

The military liaison teams also have been able to develop a good personality profile of the Soviet soldiers stationed there, and the assessment of them is mixed, according to western intelligence sources.

While some Soviet officers and leading divisions are said to be crack fighting men, a large number of Soviet soldiers, especially in the tank and infantry divisions, are judged to be mediocre. Only a week after the Nicholson shooting, Soviet infantry units in East Germany were criticized in Moscow's Army newspaper Red Star for being badly trained, poorly commanded and sloppy in field exercises.

"Soviet officers in East Germany are without doubt part of a military elite whose fighting power and combat-readiness, along with pay and benefits, are well above the average of their peers back home," said Karl Wilhelm Fricke, who has written extensively on the Soviet armed forces and is head of the East-West department of West Germany's public Deutschlandfunk radio.

Soviet Army defectors in Afghanistan who previously served in East Germany have reported immense discrepancies between conditions for the officers and for common soldiers.

The vast majority of Soviet troops are housed in decrepit barracks, isolated from the local population. They are paid far less than their East German counterparts, who are said to be scornful of the ragged, undisciplined nature of Soviet tank and infantry divisions.

During their three years in East Germany, Soviet soldiers are said to rise at 6 a.m. for a 16-hour work day and receive only one holiday per month. Several Army defectors have described the quality of food as very poor, with meat served only twice a week and most meals consisting of cabbage, potatoes, bread and tea.

Alcoholism, as elsewhere in Soviet society, is said to be an acute problem, one that is exacerbated among troops in East Germany by homesickness and isolation. Since vodka is expensive and strictly rationed, some Soviet soldiers have been known to turn to more desperate sources to satisfy a craving for alcohol. Soviet Air Force personnel in East Germany allegedly have mixed antifreeze with water and mashed apples to make ersatz booze, according to defectors.

East Germany's National People's Army, although outnumbered by their Soviet allies 2 to 1 on their own soil, are described by western military experts as much more impressive in terms of morale and command structure.

"The goose step is not the only Prussian tradition kept alive among the East German soldiers," a knowledgeable western diplomat in East Berlin said. "They are a highly disciplined force with a lot of pride, and that is a key reason why East German soldiers don't respect or get along with the Soviets."