Ten years ago this month, Willy Brandt, then West German chancellor, went to East Germany and shook hands with its Prime Minister Willi Stoph on a station platform at the yellow brick railroad terminal in the city of Erfurt.

It was a symbolic meeting suggesting the onset of detente that had been in the making since the mid-60s. West Germany was planting the seeds of a foreign policy that eventually were to branch east, through Berlin's wall to the gates of the Kremlin and then back across Poland's rivers to East Germany leading to the December 1972 basic treaty between the two Germanys.

Today, Bonn's eastern policy -- or Ostpolitik -- is firmly rooted in West German politics, having sprouted a forest of commerical and diplomatic links with the communist half of Europe.

But that development now poses a challenge to West Germany, particularly in light of renewed East-West tensions, and carries significant consequences for the strength of the entire Western alliance. The challenge is how to mesh what Bonn calls its "special relationship" to the East with its bonded loyalty to the West.

What orginally was an effort to bring the two Germanys closer together -- if not politically, than at least commercially and culturally -- has also, in effect, established a leading role for West Germany in the middle of Europe and provided Bonn with room for its own diplomatic maneuvering.

Before the Soviet invasion of Afghanistan, Bonn could always deal with the Kremlin and its allies while remaining staunchly pro-American. Moscow in turn sought to encourage Bonn's maneuvers in an effort to weaken its ties with the United States.

West German officials recognize they will not be able to carry on business-as-usual with the East bloc in the context of the current superpower chill. Their own Eastern policy can work, they say, only under the umbrella of superpower detente.

But on the assumption that a full-scale freeze in Washington-Moscow relations will be avoided, West Germany continues anxiously to look for maneuvering room toward the East.

The Afghan crisis has contributed a tone of urgency to the relationship. In his State of the Union message this week, which dealt largely with a review of Ostpolitik, Chancelor Helmut Schmidt called on East German head of state and Communist Party chief Erich Honecker to meet him "as soon as possible" in order to avoid a "confrontation on German soil" resulting from what he called a dangerous world situation.

A planned meeting between the two German leaders had to be postponed earlier this year because of the worsening of relations between Moscow and Washington. It was to be the first such high-level meeting between German leaders in a decade.

While making overtures to the East, Bonn has given repeated assurances to the West of its reliability and loyalty to the Atlantic alliance. This allegiance has never been seriously doubted by Western officials.

Indeed, while Bonn has portrayed itself as a protagonist of detente, it has also built up its military defense forces to the point where, among NATO members, its conventional strength is second only to that of the United States.

Nevertheless, one of the most popular diplomatic games in this Central European capital has become watching how Moscow tries both to badger and woo Bonn away from the West, and how the West German government often takes pains to avoid actions that might offend Moscow.

Western diplomats and German opposition leaders worry, moreover, that Bonn's closer relationship with the East has left it subject to political blackmail. It has been rumored in the press here, for instance, that East Germany may offer to reduce the age of citizens allowed to travel west -- a concession long sought by Bonn -- in return for West German participation in the Moscow Olympics.

Such an offer would likely tempt the West German government, although Bonn officials say they will resist any effort to drive a wedge between themselves and their Western partners.

Beyond complicating Bonn's relations with the West, Ostpolitik raises another worry among West Germans -- namely, that it has not gone far enough in opening up the East, has fallen short of high expectations and may have exhausted its original charter.

Sometime around the mid-1970s, the early glow went out of Ostpolitik for most West Germans. Until that time, a distinct majority preferred a policy of equal collaboration with the two superpowers. Since then, a solid majority soured on the Soviets and today take a stronger pro-Western stance, according to a recent report by West Germany's Allensbach Institute, a leading polling organization.

This shift in public opinion coincides with a more sober assessment by West German businessmen of the possibilities for trade with the East. The golden days when East-West trade increased by two-digit percentages annually -- it grew a spectacular 80 percent alone from 1971 to 1975 -- have given way to a period of belt-tightening in the East that is squeezing out much of the former dynamism.

Schmidt himself, while citing gains in trade and closer contact with the East over the past 10 years, said in his speech that it is still impossible to speak of good, or even normal, relations between West and East Germany. Essential freedoms continue to be denied to East Germans, he said, and "as long there is a wall and as long as there is violence on the border across Germany, we cannot say we are satisfied."

When Bonn launched its eastern policy, it never did accept the existence of two German nations. Because of that, policy has carried a built-in instability from the start.

West Germany did recognize East Germany as a separate state, but within a single German nation. It refused -- and still refuses -- to acknowledge East Germany as a foreign country. West Germany remains commited by its constitution to press for reunification.

Between West Germany and Poland tensions also linger. Bonn recognized Poland's long-disputed western boundary along the Older and Neisse rivers. But West German law still lays claim to Germany's 1937 national boundaries, which include territory that is now part of Poland.

These fundamental disputes were conveniently submerged in the rush to normal relations. The original program for Ostpolitik called for a series of "small steps" between Bonn and Eastern Europe, involving mostly ways of facilitating trade and human contact. The question today is whether there are many more substantial small steps left to be taken before the old disputes become major irritations once again.

"The Germans are coming to the raw nerve, to the built-in conflict," said an American diplomat experienced in German affairs. "They are approaching a point where perhaps more major steps aren't possible."

This matter is a delicate one. Politically so, because Schmidt's Social Democratic Party launched Ostpolitik and will be defending it in national elections this autumn against opposition party claims that the government has not bargained hard enough with the Soviet Bloc and entertained illusions about what Ostpolitik could achieve.

West Germans themselves appear genuinely confused about the sort of relations they want with the East, given the price of political concession that goes along.

Recent polls reflect a curious dichotomy. On one hand, roughly two-thirds regard the invasion of Afghanistan as a sign that something went wrong with detente. On the other, about two-thirds say they do not want to see Ostpolitik abandoned.

The seeming inconsistency reflects a basic conflict: most West Germans do not trust the Soviets but nevertheless want to keep negotiating for the sake of peace and stability in Central Europe.

Senior Bonn officials say privately they have dismissed the possibility of further significant developments in relations with the East for perhaps the next several years. Instead, they appear preoccupied, along with their Eastern European counterparts, with saving what has been achieved.

The list from Bann's view is substantial:

Trade. West German exports to Warsaw Pact countries tripled during the past decade, reaching $7.7 billion in 1979. Almost one-fourth of the Organization of Economic Cooperation and Development deliveries to the Soviet Bloc now come from West Germany. Meanwhile, West Germans trade with East Germany, which Bonn counts separately, about tripled since 1970 and is expected to pass $5.6 billion.

Repatriation. The 1975 Helsinki accord is regarded here as a spectacular outgrowth of Ostpolitik. In the spirit of the agreement, roughly 250,000 ethnic Germans have been repatriated from the Soviet Union and Eastern Europe in the last five years, according to the West German government.

Contact. Eight million trips were made by West Germans and West Berliners last year to relatives and friends in East Germany. In 1970 only a small number of West Germans were able to visit the East and were often subject to delays and arbitrary searches by East German border guards. Moreover, some 50,000 phone calls are put through daily now between Germans east and west. In 1970 no phone service existed even between the two halves of Berlin.

Berlin. Once the ultimate symbol of the cold war, West Berlin has adjusted to become as normal a city as possible given its amputated position in East Germany and its walled border. Lately, in fact, the city has been enjoying a renaissance, marked by increased business investment, including such new U.S. arrivals as Philip Morris, Gillette and Ford Motor Co. Significantly, too, during the Afghan crisis Berlin has remained exceptionally quiet, with the Soviets and Western powers all seemingly intent on avoiding an incident.

Peace. Although difficult to quantify, a general relaxation of tensions in Central and Eastern Europe is clearly evident.

"It became especially clear in the last few months," said Egon Bahr, one of the architects of Ostpolitik and business manager of the Social Democratic Party, "that there has grown a way of thinking and feeling in Europe East and West that realizes a common interest in maintaining the results of the last 10 years and not to endanger them."

But while tensions have eased and relations improved, the expectation that Ostpolitik would inaugurate an era of friendly cooperation between Bonn and its eastern neighbors has not been fulfilled.

The Berlin Wall remains; East Germans, with the exception primarily of aged pensioners, are still prohibited from traveling to the West; individual freedoms within the Soviet Bloc remain sharply curbed.

The process of negotiating detailed projects to fulfill the spirit of the original treaties has proved hard going.

"This is a very strenuous business," said Egon Franke, minister of inter-German affairs. "One looks for things to talk about, sounding out the other side on whether it might be possible to come up with an agreement on something. We have achieved results that could not have been thought about before. Bus as soon as a political or ideological issue is raised, there is not much we can do."

The talks go slowly, Franke said, because the East is wary of developing too strong a relationship "They are very intent on developing their own world," he said. Besides, Moscow keeps a close eye on the negotiations. It has already lost some control, within still narrow bounds, over its Warsaw Pact partners.

Bonn officials are optimistic that Eastern Europe's desire for further trade, credit, contact and peaceful relations will keep Ostpolitik alive. The policy here as well has developed a certain momentum of its own, with powerful business and political groups in West Germany having vested interests in keeping it going.

"We have reached a plateau, this is true, in the bilateral sense," said Social Democratic strategist Bahr. "The logical and political next step is in the military field. But this move must be multilateral."

Opposition leaders warn the government that in pursuit of Ostpolitik it should stay in step with the United States. "The Soviet intention has always been to produce a reaction in West Germany that says we are in a special position," said Richard von Weizsaecker, a Christian Democrat and vice president of the lower house of parliament. "The more we approach this, the more we do what the Soviets want us to do.

"My main concern is that West Germany should invite the United States to make a common assessment of the situation and to go on with detente together. The alternative leads to a regional detente.But there is no possibility of a special German detente, only of a detente in the alliance"