The Honolulu machine, to be located near Pier 1, is one of 1,500 such monitors being installed at ports, land borders and commercial facilities across the country at a cost of about $500 million.

"When it's in place, we'll be able to monitor virtually all the international cargo arriving in Hawai'i," Carter said.

In the wake of the Sept. 11 attacks, security officials here and elsewhere have worried that terrorists could use container shipments to hide nuclear material to make a "dirty bomb" or conceal an actual nuclear device. An explosion of such a device near Honolulu Harbor, which handles 95 percent of all goods arriving in the state, would cripple the island's economy, they say.

Hawai'i imports more than $3 billion in foreign cargo a year. Most of it arrives through Pier 1 near downtown Honolulu. On rare occasions when international cargo arrives through piers on Sand Island, customs officials will use smaller, portable monitors for inspection.

The monitor, which costs between $150,000 and $200,000 and looks like an oversized version of the walk-through metal detectors familiar to airline passengers, will scan containers for different kinds of radioactive material and issue an alert when anything is found.

If no radioactivity is noticed, the truck will be able to continue on its way in a matter of seconds. If an alert is issued, the truck will be moved to a nearby spot for closer inspection.

Homeland Security officials around the country have been under fire for the slow pace at which they've moved to protect ports and harbors, while airport security was tightened immediately in the wake of Sept. 11. The problem even became an issue in the presidential race, with Sen. John Kerry criticizing the Bush administration for what Kerry says is the small amount of incoming cargo inspected at American ports.

"We're moving as quickly as we can with the current funding," Todd Hoffman, a Customs and Border Protection official, told members of Congress earlier this year.

Carter said planning for the Honolulu monitor began in April with customs officials working with state and private transportation officials to identify the best location and uses of the machine.

Until next spring's installation, port inspectors will continue to use pager-sized radiation detectors and hand-held isotope identifiers to scan cargo.

"They're so sensitive that they can even tell if you have just had a medical test involving radiation," he said.

The Bureau of Customs and Borders Protection has more than 100 inspectors overseeing more than 12,000 containers that arrive here annually from foreign ports. Domestic cargo is screened at its Mainland point of departure and will not have to go through the radiation portal here.

So far, no illegal radioactive material has been discovered in Honolulu, Carter said. Most of what has been found turns out to be either medical or industrial waste with low levels of radioactivity. Some natural products, including bananas, also can set off the radiation detectors.

Unlike an X-ray machine, the new portal emits no radiation. Instead it works more like a geiger counter, providing only a radiation reading.