Prague, Czech Republic ? President Bush urged NATO allies to “come with us” and help disarm Saddam Hussein, even as summit diplomats said Tuesday the alliance will not take up arms collectively against Iraq.

Bush, arriving first among 19 NATO leaders for a two-day gathering shadowed by intense security, said alliance nations can find ways individually to support his campaign against Saddam.

“Everybody can contribute something,” he told Czech TV as White House aides sought to lower expectations for concrete action by NATO against Iraq.

“It all has got to be done within the strategy of the true threats we face in the 21st century, which is global terrorism. That’s the biggest threat to freedom right now,” Bush said.

NATO intends on Thursday to create a 21,000-strong rapid response force that could mobilize in seven to 30 days to confront threats from terrorists, renegade governments or regional crises.

In a historic reach toward Russia, the alliance also plans to invite seven former communist states into NATO – Lithuania, Latvia, Estonia, Romania, Slovenia, Slovakia and Bulgaria.

The threat of terrorism loomed over the summit as the Czech government mobilized 12,000 police officers, 2,200 heavily armed soldiers and special anti-terrorist units to protect the presidents and prime ministers.

A U.S. F-16 fighter jet takes off from the Czech air force base at Caslav. Fighters of the USAF 31st Wing based in Aviano, Italy, will help to guard Czech air space during the NATO summit this week in Prague.

Engines growling from above, U.S. warplanes helped Czech airmen in small, aging Soviet-era planes protect the Prague airspace. Intelligence officials fear the leaders are an inviting target for al-Qaida and other terrorist organizations.

Threats surrounding a Bush speech to students today about the planned NATO force were so serious that it was moved from Radio Free Europe’s headquarters to a sequestered hotel along the riverfront, law enforcement officials said.

“Terrorist attacks can happen wherever and whenever,” Czech President Vaclav Havel said. “Our police and security forces have prepared a wide network of measures and have done the maximum so that nothing like that would happen. But 100 percent certainty cannot be found in the world today.”

Railway workers found an explosive device on railroad tracks within the city limits while checking a section of track that appeared to have been sabotaged, police spokeswoman Eva Brozova said.

Police are worried, too, about how to handle the thousands of protesters who have said they will demonstrate.