In German it is called an unding, literally a "non-thing," a term applied to monstrosities and absurdities. But seen from the west, the Berlin Wall -- which will be 20 years old Thursday -- can be deceptive.

It looks unimposing, a barrier of plain 10-foot high, dirty-white concrete panels. A pipe runs along the top, its slippery curved surface intended to foil grabs by refugees attempting to leap into the western, democratic part of Berlin.

But such tries are rare nowadays. Seen from the east, the reason becomes clear. The barrier is menacing and deadly efficient. It begins about a hundred yards before the concrete slabs with an electrified fence, followed by a seeming overindulgence in security devices -- ditches, guard towers, guard dogs, patrol bunkers, spotlights, trip wires and planted objects that are large and heavy enough to stop a tank.

East Germany, in a continued effort to justify the wall's construction, calls it a "barrier against imperialism and revanchism."

For the West, the 101-mile encirclement of West Berlin survives as a lasting and brutal symbol of the cold war. Its anniversary has been marked by articles in the West German press recalling the shock, the sufferings of the Berliners and the inaction of the Western allies at the time it went up. There will be marches and vigils Thursday in the western part of the city, angrily and somberly honoring those memories and the victims of the wall.

There will be marches and speeches in East Berlin as well, highlighted by an anticipated tough message from East German Communist Party chief Erich Honecker who, on Aug. 13, 1961, was the Politburo member responsible for overseeing construction of the wall.

In an effort to turn the day into a national celebration, the Communists have hung red flags and East German banners on shops, houses and government buildings. The occasion is meant to glorify what is described as an important protective step in the development of the country, and East Germans have been urged in party newspapers to remember "border guard heroes" and to mark the "20 years of the antifascist protection wall."

Stefan Doernberg, the East German party historian, recently portrayed the wall as an important milestone on the way from cold war to detente. It helped stabilize East-West relations, he said. This view is widely shared in the West. For all the resentment the wall engendered among West Germans, it did put a comparatively unbloody end to the mounting flight westward of East German refugees that was threatening to destabilize the Soviet-led East Bloc.

The history books say today that some senior Western officials, including President John F. Kennedy, suspected the East Germans would build a wall in Berlin, though no one appears to have guessed when.

In those early Sunday hours when the first barriers appeared, Willy Brandt, then governing mayor of the western sectors of Berlin and later chancellor of West Germany, was riding in the sleeping car of a train enroute from Nuremberg to Kiel. French President Charles de Gaulle had gone on a weekend outing at his country residence and British Prime Minister Harold Macmillan was bird-hunting in Scotland, while President Kennedy had settled in for a weekend of sailing and relaxing at his family's compound in Hyannis Port, Mass.

East German troops began the wall's construction, and by dawn the first day they had hastily strung barbed wire fences and rushed other obstacles into place to block traffic between East Berlin and West Berlin. Three days later, after the Western allies had shown they would not risk a war with the Soviet Union to knock down the barrier, East Germany started pouring concrete along Berlin's dividing line.

Since then, the wall's fortifications have been progressively strengthened. The same is true of the wire mesh and other barriers that block the 856-mile border between East Germany and West Germany.

Inevitably, the Berlin Wall anniversary stirs talk in West Germany of eventual reunification -- a prospect now generally placed in the distant future, if ever. The Bonn government would be happy just to see Chancellor Helmut Schmidt meet Honecker in East Germany -- a summit meeting that was postponed twice last year, first because of the Soviet invasion of Afghanistan and then by the labor upheaval in Poland.

While Berliners themselves may never accept the wall in their city, it has long since ceased to be a crisis for them. Both the city's island existence inside East Germany and its division preclude a sense of complete normality, but the concerns of the 2 million Westerners who live here today are largely those of inhabitants of a normal big city.

Noting this evolution, the German press has made much of the graffiti that appears today on the western side of the wall. The messages are said to have lost the angry, polemical tone of the 1960s and early 1970s, turning whimsical and ironic.

When the wall speaks now, it says such things as: "Attention: next Coke, 10,000 km kilometers ," or "Jump over and join the party," or "Warning: East German high jump training area."

Also amid the wall's scribbled cartoons and symbols is this simple statement: "Made in Germany."