WASHINGTON (AP) _ Marvin Cantor is a victim of German unification.

Cantor's architectural firm spent two years designing plans to build a Washington embassy for East Germany. As he was drawing the last walls, the first crack was made in the Berlin Wall.

East Germany, rapidly advancing toward union with its neighbor to the west, soon will cease to exist. Without a country, who needs an embassy?

West Germany has a sprawling embassy on a verdant hill in northwest Washington. The East Germans have occupied one floor of an office building on the city's Embassy Row since establishing diplomatic relations with the United States in 1974.

But the East Germans always viewed their quarters as temporary and sought an embassy building befitting their position as the nub of the Warsaw Pact and a major economic power in the Soviet bloc.

In the early 1980s, the East Germans leased a lot in a planned complex of some two dozen embassies on International Drive, where several governments - including Ghana and Israel - already have moved.

After another period of inactivity, East Germany commissioned Cantor's firm in early 1988 to design the new embassy offices, or chancery building as it's known in diplomatic parlance.

Cantor completed the blueprints late last year. The East Germans were pleased, he said.

The building would cost $6 million to $8 million to build and would occupy about 45,000 square feet.

A full political union of the two Germanys is expected next year, but the sisters already have agreed on a treaty merging their economies.

In a sign of things to come in Washington, the two embassies - once separated by several miles of real estate and four decades of rival ideologies - will hold their first joint function Monday with a screening of a television documentary on composer Johann Sebastian Bach.

The final decision on the fate of the embassy project is still before the newly elected non-Communist government - the first, and probably last, East Germans will know.

''It has to be reviewed,'' said Peter Janz, first secretary of the East German embassy. He said a decision was expected soon.

Cantor believes that once the new government resolves the myriad pressing problems bedeviling the logistics of unification, it may suggest to West Germany that his plans be modified for an annex or consular section for the embassy of the unified Germany.

''Maybe that's just wishful thinking,'' he said.

Either way, he has nothing to worry about.

First, he expects to be paid.

Second, for every country dropped from the U.S. diplomatic roster, a new one is tacked on. Cantor could be commissioned to build an embassy for Mongolia, which recently established diplomatic relations with the United States.