The detectors look like small pagers and vibrate or beep when within 50 feet of radioactive material.
In addition, the devices can detect some chemical substances associated with weapons of mass destruction, and are so sensitive they may react to cancer patients who are undergoing radiation therapy or chemotherapy.
The deployment comes amid the continuing war on terror and as the United States moves closer to war with Iraq.
The completion of the deployment also coincided with the release this week of a new CIA assessment. The agency said that the Saddam Hussein regime might conceivably counterattack the United States with weapons of mass destruction, possibly through third-party terrorists, if this country attacks Iraq.
In the same vein, other emergency measures include a recently publicized Bush administration plan to inoculate the American public if the United States is attacked with a biological weapon containing smallpox.
As first reported by UPI this year, U.S. Customs inspectors have worn the radiation devices voluntarily for at least three years -- following a 1998 presidential directive -- but their use has been expanded to federal law enforcement agencies, starting with the Secret Service, which guards the president and the White House.
Now agencies such as the Capitol Police have been trained in their use and are carrying the devices.
President Bush cited the devices in a Houston speech this month. The president said the union representing the Customs agents wanted to keep use of the detectors voluntary, despite the national war against terrorism and a new Customs regulation requiring that they be worn. Bush said this was one reason why he needed flexibility to make personnel decisions in the proposed Department of Homeland Security, which would include the U.S. Customs Service.
The National Treasury Employees Union, which represents Customs agents, responded by saying that there had been no such dispute, that it supported the mandatory use of the detectors and that the only concern it ever raised was to make sure there had been adequate training.
Despite that contretemps, the use of the detectors is widespread among federal security agencies, with many of the devices being deployed as late as this week.
Earlier this year, administration sources said they had intelligence that al Qaida -- the militant group held responsible for the Sept. 11, 2001, attacks against the World Trade Center and the Pentagon -- was planning to use radioactive material in an attack against the United States.
One scenario reported by intelligence agencies would be an attempt to "decapitate" the U.S. government by detonating a weapon of mass destruction in Washington.
A U.S. citizen named Jose Padilla was arrested in May as he re-entered the United States at O'Hare International Airport in Chicago.
Government officials say Padilla received training at al Qaida camps in Afghanistan, and was plotting with the remaining leaders of the terrorist organization to set off a radioactive "dirty" bomb -- a conventional explosive device wrapped in radioactive material -- in an unspecified American city.
Investigators said the alleged conspiracy never really got beyond the planning stage.
Padilla, who now calls himself Abdullah Al Muhajir, has been classified an "enemy combatant," and is being held without access to a lawyer in a Navy brig in South Carolina.
In a related development, the Justice and State departments announced this week that they have begun to plan "domestic preparedness exercises" to see how the nation will respond in the event of an attack using weapons of mass destruction.
The congressionally mandated response exercise, "Top Officials 2," or "TOPOFF 2," is scheduled to take place in the Chicago and Seattle metropolitan areas in May.
Canadian officials are scheduled to join their U.S. counterparts in the exercises.