OTTAWA — Up to 40 RCMP cruisers patrolling the capital will be fitted with "dirty bomb" detectors amid rising fears of a terrorist strike involving radiological weapons.

The system is intended to provide early warning of a pending attack, giving police a chance to locate a deadly device before it can be detonated near Parliament Hill or another prominent Ottawa site.

"When the radiation background level rises above normal an alarm will sound," says a description of the detection system published by the Mounties. "This will allow for immediate action by police and other emergency personnel."

The RCMP will advise federal officials on installation of the detection technology in the patrol cars and train officers to use the units.

The vehicles are considered an ideal spot for the devices in order to ensure widespread monitoring of potentially vulnerable landmarks in the capital area.

The project underscores the degree of concern in federal security circles about the possibility of an attack involving radiological materials in the wake of the Sept. 11, 2001, terrorist assaults on the United States.

Officials are particularly concerned about a so-called dirty bomb packed with conventional explosives such as dynamite to scatter radioactive material.

The initial blast can kill or maim bystanders, while the radioactive fallout may claim more victims. In addition, the resulting contamination would place the area off-limits to people for lengthy periods, causing panic and wreaking economic havoc.

A dirty bomb could be made from a softball-sized amount of radioactive material pilfered from a medical laboratory, industrial operation or nuclear-fuel disposal site.

Documents discovered in the Afghan city of Herat early last year indicated Osama bin Laden's al-Qaida network may have successfully assembled a modest dirty bomb.

The new detection units will include radiation sensors that work in tandem with global positioning technology, cellular communication and mapping devices to report radiation readings to a central monitoring post. A prototype of the system was unveiled recently at RCMP headquarters.

The initiative, funded through the federal anti-terrorism budget, is a collaboration between the Mounties, the Health Department's radiation protection bureau, the Geological Survey of Canada and private industry.

The project is part of the federal science community's effort to beef up chemical, biological, radiological and nuclear counter-terrorism preparedness, known as the CBRN Research & Technology Initiative, or CRTI.

A CRTI summary of the project warns the psychological impact of a dirty bomb attack on a Canadian city could be severe.

"Significant radiological resources could be acquired by terrorists through clandestine theft or low-level military operations and moved, possibly undetected, to urban population areas or to targets of high symbolic value."

Such targets in the national capital region might include high-profile locales such as the Parliament buildings, the Supreme Court of Canada or the United States embassy.

The RCMP and CRTI referred inquiries to the Health Department. A Health official involved in the project was not immediately available.