BERLIN, OCT. 3 -- The new capital of a new nation was one massive street festival today, as governments around the world welcomed the united Germany with varying degrees of warmth and concern and Germans reveled in the first celebration of their new national holiday, German Unity Day.

"Since midnight, the Germans live together in one state," began the anchorman on tonight's ZDF national TV news. Wearing a tie with a German flag pattern, he continued, "The German Democratic Republic {East Germany} is no more."

Waking from a late-night party that police said attracted more than 1 million people, Berlin this morning was host to a stately ceremony at which President Richard von Weizsaecker appealed to the 79 million Germans to learn to adjust to their differences.

"Uniting means learning to share," he said. Von Weizsaecker urged West Germans to respect the courage of East Germans who rose up against their repressive regime. And he asked all Germans to reflect on the Nazi Holocaust, "this most awful of all crimes."

In a message to the nations of the world, Chancellor Helmut Kohl promised that "only peace will emanate from German soil in the future."

From Washington to Warsaw, Kohl's words and the Germans' whirlwind rush to unity were welcomed.

"The desperation and scars cannot be erased from our minds," said Vaclav Havel, president of Czechoslovakia, a nation that suffered from Nazi aggression. "But it is necessary and possible to overcome them."

But British Prime Minister Margaret Thatcher, an early and persistent critic of unification, said that despite her official congratulations to Bonn, "it will be up to the rest of us to see that Germany does not dominate. Others of us have powerful voices."

Israeli Prime Minister Yitzhak Shamir said he hoped his country and Germany would continue to have good relations, but he noted his disappointment that the unity agreement between the two states made no mention of the Nazi slaughter of Jews.

The Polish ambassador to Bonn, Janusz Reiter, said, "Poland has no fear of a united Germany."

But on the German-Polish border, where Poles faced a new visa requirement today, tensions between the two countries flared when Germans threw stones and attacked the cars of Poles returning home from their last visa-free shopping expeditions to the West.

Authorities in Bonn moved quickly today to emphasize the end of the other Germany. Just after midnight, police went to arrest Werner Grossmann, the last chief of East Germany's espionage agency. But Grossmann was gone. On his desk, police found a West German newspaper opened to a story about his impending arrest.

Later today, police found Grossmann and arrested him, according to the federal prosecutor's office.

Authorities also went after Markus Wolf, the legendary East German spymaster who has drifted back and forth between Moscow and East Berlin since last fall's revolution. Wolf, who ran his country's intelligence agency from 1967 to 1987 and once planted agent Guenther Guillaume as a top adviser to then West German Chancellor Willy Brandt, was Bonn's prime target for arrest.

But Wolf was gone by the time police arrived today. Prosecutors had warned for weeks that they would arrest him after unification, and Wolf had made equally public comments about his intention toleave the country and then try to arrange some kind of amnesty.

Even on a holiday, smaller signs of the disappearance of East Germany were everywhere.

Knots of people gathered outside office buildings in the eastern part of Berlin to stare at new signs announcing the presence of government offices moving from the old West German capital of Bonn. The bulk of government functions will remain in Bonn until after a new parliament is elected in December.

The luxury train that former East German Communist leader Erich Honecker had built for himself was brought out of mothballs to serve as overflow housing for the thousands of journalists who came to Berlin to cover the unification.

German TV tonight offered a documentary on unification titled "The Fourth Attempt," a reference to the Germans' relative inexperience with national unity. The Holy Roman Empire, formed by Charlemagne in 800, contended with up to 234 principalities and floundered through a millenium of constantly shifting alliances and borders.

Not until 1871 was some semblance of German unity achieved when Otto von Bismarck created a Prussian empire. And only today were the Germans finally able to boast of a nation united peacefully and democratically.

The West German flag flew over landmarks of the collapsed communist state. Even the East German Council of State building, where top Communists held sway until early this year, was topped off by a black, red and gold banner -- bereft of East Germany's hammer-and-compass insignia -- fluttering in the soft wind of a stunning, cloudless day.

There was also a bit of good news for the millions of East Germans who have lost their jobs in the instant transition to a market-based economy. A survey of West German companies found that about half of 500 firms polled plan to invest in the former East Germany by the end of 1991.

Not all the day's events were solemn official affairs. A group of leftist artists announced the founding of the Autonomous Republic of Utopia on a "Day of German Impunity." They celebrated their alternative unification by wearing masks of Chancellor Kohl's face and singing their anthem, "Deutschemark, Deutschemark Ueber Alles," a satirical attack on the competitiveness and material concerns of West German society.

A group in Bonn was formed today to lobby for the re-division of Germany. The Directorship for a Separated Germany said that because German politicians have not learned from the troubled history of their nation, and because the addition of East Germany to the country will bring social and economic problems, Germans should fight to restore the division.

Fringe groups, including anarchists and neo-Nazis, clashed with police in several cities. Police in Berlin, Bonn, and Frankfurt reported more than 300 arrests after extremists threw stones and firebombs at police and shop windows. About 10,000 demonstrators chanted "Never Again Germany!" as they marched through Berlin streets.

But for most Germans it was a day of celebration.

On Unter den Linden, Berlin's grand boulevard, a throng gathered around two policemen standing side by side in a doorway, one dressed in gray, the other in blue.

Until midnight, each officer had worked for a different Germany. They spent this afternoon guarding the former British Embassy to the former East Germany and posing for snapshots as one parent after another placed a child between the officers to create a personal memento of German unity.

"Why the different uniforms?" asked someone in the crowd.

"I'm from drueben {over there}," the officer from the West said, using the term that Germans have used for years to indicate whichever Germany they were not in.

A pedestrian, Heinz Richter, heard that and stopped dead. He turned to the policeman and exclaimed, "Drueben! There's no such thing anymore."