BONN, JUNE 26 -- A united Germany could resume its place as a single nation stretching from France to Poland in just over five months, the West German government announced today.

Looking beyond Sunday's economic merger of East and West Germany, Bonn's Interior Ministry released the first details of a plan to complete the two countries' political unification on Dec. 9, when the first democratic all-German elections since 1933 are tentatively scheduled.

The plan, which suggests the specific wording of East Germany's application to become part of West Germany, is the first official sign of how far the Bonn government has progressed in its drive to stitch together the nation split by its World War II opponents.

The government proposal is also, opposition leaders say, a political tool intended to strengthen Chancellor Helmut Kohl's Christian Democrats by turning the December vote into a virtual referendum on unification -- enabling the chancellor to portray his opponents as foes of the motherhood-and-apple-strudel issue of German unity.

At midnight after the common election day, the two Germanys would become one nation operating under West German law, according to Interior Minister Wolfgang Schaeuble. He said negotiations toward a treaty on political unity will begin this week in East Berlin.

That treaty, like the detailed plan for economic merger approved by both parliaments last week, would spell out how to bring the East German legal and political system in line with West German laws. Schaeuble said he expects the political treaty to be ready in September.

Despite the growing optimism of a West German government anxious to complete unification while Soviet President Mikhail Gorbachev retains his position, numerous obstacles remain before the two Germanys can become one.

Schaeuble, like Kohl and East German Prime Minister Lothar de Maiziere, envisions that the East Germans will become part of West Germany under a section of the Bonn constitution allowing East Germany's five states to apply to the West German government for admission. But before that can happen, the East German government must recreate the states, which were dissolved and rearranged by the Communist regime.

Even then, the proposed December election raises difficult legal problems. Schaeuble said that to speed the process, the two countries could conduct elections on the same day under their existing election laws, and the winners would sit together in one parliament.

But the West German opposition Social Democrats said today that quick unity is "not acceptable" if the two countries retain their considerably different election systems.

In West Germany, political parties must get 5 percent of the vote to win seats in parliament -- a measure designed to keep extremist parties out. The new East German voting system -- used only once, to choose the first post-Communist government elected in March -- allows representation for all parties.

Under the West German plan, the East Germans elected in March would serve only nine months of their terms. New deputies would almost certainly be chosen primarily from among the West German parties, which plan to become all-German parties this fall.

Another obstacle to final unification this year is the question of the capital. Opinion polls in both Germanys show overwhelming majorities favoring Berlin as capital of a united nation. And both de Maiziere and the mayors of both sides of Berlin demanded this week that the former capital again assume its historic role in place of Bonn, West Germany's "provisional" capital since the end of World War II.

Schaeuble said the question of the capital should be delayed until after unification to assure that the process is completed this year. The West Germans also want to delay resolution of several other controversial differences between the two countries, including abortion, which is legal in East Germany and largely illegal in West Germany.

The West German plan, contained in a 15-page "discussion paper," would allow the joint German parliament to consider constitutional changes only after unification is complete. The East German parliament would be dissolved and the East German prime minister would become a temporary member of the West German cabinet.

The rush to create a single Germany before such major structural changes are discussed stems largely from the uncertain situation in the Soviet Union, Bonn officials said.

Kohl is said to argue that Germany must maintain the momentum toward unity so the Soviets cannot hope to block the historic change, despite the complaints of some Soviet politicians that Gorbachev is giving away Moscow's most valuable and strategically crucial ally.

The West Germans also believe that domestic initiatives toward unity will speed up Soviet cooperation on the international aspects of recreating a single Germany. The Soviets have not yet agreed to allow a united Germany to become a member of the North Atlantic Treaty Organization, and the presence of 380,000 Soviet troops on East German soil remains the single greatest sticking point in arranging the defense and government of the new Germany.