PRAGUE — President Obama said that North Korea violated international rules when it tested a rocket that could be used for long range missiles, and called on the Security Council to take action.

Todd Heisler/The New York Times

President Obama said that North Korea had broken global rules in launching a rocket over the Pacific in a speech in Prague on Sunday. More Photos >

“This provocation underscores the need for action—not just this afternoon at the U.N. Security Council, but in our determination to prevent the spread of these weapons,” Mr. Obama said. “Rules must be binding. Violations must be punished. Words must mean something.”

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Response to the Rocket Launch

Mr. Obama’s comments on North Korea were delivered at the end of a historic speech before more than 20,000 people here that had been planned far in advance to lay out Mr. Obama’s plans to stop the spread of nuclear arms.

Mr. Obama also said that he still plans to continue with plans to pursue missile defense, but tied the need for such a system to any Iranian acquisition of nuclear weapons. Russia opposes locating a defense shield in Poland and radar system in the Czech Republic, as current plans call for, and Mr. Obama said in a letter to President Dmitri Medvedev two months ago that if Russia is able to successfully help the United States stop Iran from getting a nuclear weapon, there will be no need for a missile defense shield in place in Eastern Europe.

The issue has particular resonance here in Prague, since the collapsed government of Prime Minister Marek Topolanek, which suffered a parliamentary vote of no confidence ahead of the visit, went to bat against popular opinion to support installing the radar system here, only to have the Obama administration begin to walk back from the plan.

Mr. Topolanek last week got back at Mr. Obama when he called Mr. Obama’s economic stimulus proposals “a way to hell.”

Mr. Obama came to Prague anyway, although his speech stuck largely to arms control and proliferation, without veering too far into economics.

“Let me be clear: Iran’s nuclear and ballistic missile activity poses a real threat, not just to the United States, but to Iran’s neighbors and our allies,” Mr. Obama said. “The Czech Republic and Poland have been courageous in agreeing to host a defense against these missiles. As long as the threat from Iran persists, we will go forward with a missile defense system that is cost-effective and proven.”

That North Korea fired a rocket over Japan and into the Pacific just hours before Mr. Obama’s speech lent his message an added urgency, Mr. Obama said, although White House officials disputed any suggestion that the secretive government in the North timed its rocket launch to coincide with Mr. Obama’s speech.

“I hate to speculate about North Korean motivations,” said Gary Samore, the White House coordinator for nonproliferation, adding that the North Koreans had announced their launch window two weeks ago, and that weather conditions favored today. “I’m not sure this is a deliberate calculated action on the part of the North Koreans.”

In any case, the North Korean action illustrated again that the international community has mostly had its hands tied when it comes to stopping North Korea’s pursuit of nuclear weapons. The Security Council may slap Pyongyang on the wrist, as it has before, but China, a permanent member, has often stood in the way of strong international action.

Nonetheless, Mr. Obama said he will push for strong Security Council action. “Now is the time for a strong international response, and North Korea must know that the path to security and respect will never come through threats and illegal weapons.”

But it remained unclear exactly what the West will be able to do by way of the talked about punishment. President Bush pressed for similar sanctions after the North’s nuclear test in October 2006, but those sanctions had little long-term effect.

Although some Czech officials had even quietly discouraged Mr. Obama’s speech, worried that it would intensify the Czech public’s fears of being caught between the United States and Russia. But the crowd of Czechs here mostly seemed transfixed.

Irena Kalhousova, 30, a lecturer in international relations, who said she woke up at 4 a.m. to make sure she could get a glimpse of Mr. Obama, said she had been struck by the contrast between the detached haughtiness of Czech President Vaclav Klaus, 67 — who was booed when his face appeared on a screen —and the youthful vigor of Mr. Obama, whom she said radiated “positive energy”.

Mr. Klaus, an iconoclast with a perfectly clipped mustache, has blamed what he calls the misguided fight against global warming for contributing to the international financial crisis. The crowd cheered — and Mr. Klaus appeared to grimace — when Mr. Obama said the United States was ready to lead in the global fight against climate change. The evening before, Mr. Klaus appeared to have been snubbed when Mr. Obama opted to dine privately with the First Lady rather than attend a state dinner with the Czech President.

“Our President Klaus looks bored, old and angry while Mr. Obama is young, energetic and inspiring,” she said. “It would have been nice to have a stable government in the Czech Republic,” she said, alluding to the recent collapse of the Czech government. “But I feel we have redeemed ourselves in front of the world today.”

She said that before the speech, she had feared Mr. Obama was too soft on Russia and too naïve when dealing with rogue states. But she said Mr. Obama’s indication that he was still open to installing a missile defense radar system in the Czech Republic had helped reassure her, along with his strong warnings to North Korea and Iran that nuclear armament would not be tolerated.

Jakub Fidler, 21, student of political science, said he had been so excited about Mr. Obama’s appearance, he had left his town of Bohumin, in the eastern part of the country, before midnight, to catch the last train to Prague, where he arrived at 4 a.m. “Obama to me is a symbol of change, he is a break from the norm and not part of the old establishment,” he said. Our politicians could learn a thing or two from Obama, especially when it comes to being polite and how to behave on the international scene.”

Not all were effusive about Mr. Obama’s appearance. Miloslava Krulova, 76, who worked in a bank before she retired, said she was worried that Mr. Obama’s disarmament drive could prove detrimental to global peace.

“I came here today because I admire Obama’s intelligence. He is also a good husband and father. But I am skeptical of his words because trying to get the world to disarm might have the opposite effect.” Noting the throngs of mesmerized youth, she added: “I was shocked that I seemed to be the only elderly lady here. Maybe people of my generation are afraid, that they might not understand Obama and his policies.”

Jan Krcmar contributed reporting.

www.nytimes.com/2009/04/06/us/politics/06prexy.html