BONN, JULY 16 -- President Mikhail Gorbachev's surprise agreement to German unification with membership in NATO cemented a new partnership from which both the Soviet leader and West German Chancellor Helmut Kohl expect rich payoffs, according to political observers across Europe.

The German-Soviet agreement announced today is the latest in a rapid-fire series of victories for Kohl, who could not stop smiling at his press conference with the man who for many months stood between the chancellor and his goal of creating a single Germany this year.

For Kohl, the breakthrough is a political coup, a chance to upstage his foreign minister and rival for historical notice, Hans-Dietrich Genscher. Gorbachev's green light removed the last obstacle to all-German elections this December -- something Kohl seeks both to achieve a national goal and to improve his own reelection chances.

"The new Europe has taken a concrete shape," said Volker Ruehe, party secretary of Kohl's Christian Democratic Union.

"Chancellor Kohl has done rather well for himself," said Col. Andrew Duncan of London's International Institute for Strategic Studies (IISS). "The expectation was that Gorbachev would hang on a little longer and perhaps get the chancellor worried that his election would not occur on time."

Gorbachev's decision -- which he described as an act of "realpolitik," the German term for expediently accepting political facts -- startled U.S., British and French diplomats, many of whom expected the Soviets to accept German membership in the Western alliance only at the last minute and only after extracting even more concessions from the West Germans.

But for Gorbachev, satisfying Kohl now puts the Soviet leader in the strongest possible position to seek more Western aid later, said Angelika Volle of the German Society for Foreign Policy.

"He figures now the Germans owe him," she said. "And don't forget his dream of a common European home. This move brings him closer to that dream than ever."

At NATO headquarters in Brussels, news of Gorbachev's change of heart was welcomed as a sign that the alliance will retain its role as the essential glue binding Western nations. "The unification of Germany means that the division of Europe is also being overcome," a spokesman said.

But Western diplomats around Europe tonight seemed skeptical of the Kohl-Gorbachev announcement, wondering whether Kohl had privately promised to push for future troop cuts or removal of nuclear weapons from German soil -- two goals that topped the Soviet agenda throughout unification talks.

"It's not enormously elegant for just the two of them to announce this," a British diplomat said, "but unless Kohl has gone further than previously advertised in his concessions, this is a breakthrough."

West Germany's NATO allies said Kohl has now achieved what the Western alliance wants, four months before the scheduled finish of the international talks on German unity. Those talks continue Tuesday in Paris with a discussion of Polish concerns about the Polish-German border.

The Soviet leader's misgivings about a united Germany remain clear. "Whether we like it or not," he said, "the time will come when a united Germany will be in NATO. . . . In absolute terms, we in our turn did not get what we had been counting on. But we were realists."

But Gorbachev, emboldened by his success at last week's Soviet Communist Party congress, apparently decided to act now rather than give in at the final moment and be accused of "losing Germany."

"Gorbachev was so delighted to get the Communist Party off his back that he felt free to do this now," Duncan, of the IISS, said. "With both the head of the Soviet Army and the head of the KGB no longer in the Politburo, Gorbachev has got much more power than he had before last week."

For months, the Soviets have played a frustrating game of diplomatic cat-and-mouse, refusing to agree to NATO membership for a united Germany and insisting variously that the new nation must retain East Germany's Warsaw Pact membership or that unification must await the signing of a peace treaty officially ending World War II.

Today, there was no mention of any of the points Gorbachev had pushed all year. Instead, there was a smiling, warm Soviet president who had made the German chancellor the first Western leader to visit his home region in the Caucasus.

"I'm surprised it took so little to bring Gorbachev around," Volle said. "He needed a face-saving measure to accept Germany in NATO and apparently the NATO communique was sufficient."

NATO leaders earlier this month invited Gorbachev to visit them and presented him with an outline of a new, less threatening, more political Western alliance.

British Foreign Secretary Douglas Hurd and his French counterpart, Roland Dumas, tonight credited the changes NATO made for sending the Kremlin the message it needed to hear.

Kohl has negotiated directly with the Soviets even as the four victorious World War II powers and the two Germanys held their own unification talks. He emerged from the NATO and Houston economic summits this month with a package of military and financial concessions for Gorbachev.

The Allies have told Kohl that he is free to make his own concessions to the Soviets, and that is exactly what the Germans did.

Although the United States, Britain and Japan opposed massive financial aid for the ailing Soviet economy, the West Germans delivered $3 billion in state-guaranteed loans, along with a full program of technical support and a promise to pay the expenses of the 360,000 Soviet troops that will remain in East Germany for three to five years.

And now Kohl has also agreed to place voluntary limits on the future strength of the German military. The combined East and West German forces now number about 600,000; Kohl agreed to a ceiling of 370,000, also to be accomplished over the next three or four years.

Because he could not speak for the other Western allies, Kohl did not achieve any cut in the World War II powers' presence in Berlin. British, French and American troops would be asked to remain in Berlin for as long as Soviet troops stay in the former East Germany, Kohl said.