Washington ? With huge New Year’s Eve celebrations and college football bowl games only days away, the U.S. government last month dispatched scores of casually dressed nuclear scientists with sophisticated radiation detection equipment hidden in briefcases and golf bags to scour five major U.S. cities for radiological or “dirty bombs,” according to officials involved in the emergency effort.

The secret call-up of Department of Energy radiation experts to Washington, New York, Las Vegas, Los Angeles and Baltimore was the first since the weeks after the Sept. 11, 2001, attacks.

Even now, hundreds of nuclear and bioweapons scientists remain on high alert at several military bases around the country, ready to fly to any trouble spot. Pharmaceutical stockpiles to treat biological attacks were loaded on transportable trucks at key U.S. military bases.

One of the U.S. officials’ main fears was of a dirty bomb, in which a conventional bomb is detonated and spews radioactive material and radiation across a small area. Security specialists say such weapons are unlikely to cause mass casualties, but could cause panic and devastate a local economy.

On the same day that Ridge raised the national threat level to orange or “high,” from yellow or “elevated,” the Homeland Security Department sent large fixed radiation detectors, and hundreds of pager-sized radiation monitors for use by police in Washington, New York, Los Angeles, Las Vegas, Chicago, Houston, San Diego, San Francisco, Seattle and Detroit.

Homeland Security also ordered scores of Energy Department radiation experts dispatched to cities planning large public events. One of them was Baltimore, where Coast Guard and Energy personnel patrolled the waterfront with sophisticated radiation detectors in preparation for a New Year’s Eve party at the Inner Harbor.

Dozens of others fanned out in Manhattan, where, on New Year’s Eve, up to 1 million people were scheduled to gather in Times Square. Still others converged on Las Vegas, home of a huge yearly New Year’s Eve party on the Strip, and to Los Angeles, where the Rose Bowl parade on New Year’s Day draws as many as 1 million people.

The Energy scientists arrived at their assignments to take covert readings on their disguised radiological equipment in a variety of settings.

“Our guys can fit in a sports stadium, a construction site or on Fifth Avenue,” one Energy Department official said. “Their equipment is configured to look like anybody else’s luggage or briefcase.”