At a checkpoint leading to the US-protected Green Zone, Gordy stands sentry. The affable Belgian Malinois has a nose finely tuned to detect the nitrates, plastic explosives, gunpowder and detonation cords that suicide bombers use to blow up people.

On a barren stretch of road in northern Iraq, a dog rigged with explosives approaches a group of Iraqi police officers. Detonated by remote control, the bomb tears the dog apart but doesn't harm the cops. In a war where the line between civilian and soldier is blurred, even man's best friend has been caught up in the combat.

US forces hail their trained dogs as heroes, but to insurgents, canines provide the means for a more sinister goal.

Iraqi police cite the recent use of dogs rigged with explosive devices in Latifiya, just south of Baghdad, in Baqubah in central Iraq and in and around the northern city of Kirkuk.

Some Iraqis are horrified by the ethics of dragging the animal world into a human conflict.

''How can they use these lovely pets for criminal and murderous acts?'' asked Rasha Khairir, 25, a Baghdad stockbroker. ''A poor dog can't refuse what they are doing with him because he can't think and decide.''

Despite a common prejudice in the Muslim world against dogs, which are considered unclean, even the most virulent clerical opponents of the US presence in Iraq have decried the use of canines as proxies in the war.

Abdel Salam Kubaisi, a spokesman for the Muslim Scholars' Association, a hard-line Sunni Arab clerical organization sympathetic to insurgents, called the practice un-Islamic.

``Our religion does not permit us to hurt animals,'' he said, ``neither by using them as explosive devices nor in any other manner.''

US troops extol the virtues of their canine allies in the war against the insurgents. ``Dogs are vital in Iraqi counter-insurgency efforts,'' said Staff Sergeant Ann Pitt, 35, a US Army dog handler based near the southern city of Nasiriya. ``We have many items to help us do our mission, but I don't think we have a better detection tool than a dog,'' said Pitt, who cares for Buddy, another Belgian Malinois, a dog similar to a German shepherd.

``These dogs are amazing. They are more dependable and effective than almost anything we have available to us.''

The army has deployed dogs since World War I to locate trip wires, track enemies, stand guard at base perimeters and search tunnels for explosives or booby traps.

Even these dogs weren't always treated kindly. Of 4,300 dogs sent to Vietnam, 2,000 were handed over to the South Vietnamese army and 2,000 were put to sleep. Only 200 managed to make it home, said Ron Aiello, Vietnam War-era dog handler who runs US War Dog, a 1,100-member New Jersey-based organization.

His group set up a Web site to raise funds for a memorial to honor the dogs and their handlers. In Iraq, dogs like Gordy and Buddy are posted at checkpoints and at entrances to government buildings.

They sniff for explosives among reporters' equipment at news conferences and passengers' bags at Baghdad's international airport.

``What we do is prevent people from getting killed,'' said Artwell Chibero, Gordy's 29-year-old Zimbabwean handler, an employee of a private security firm hired by the Defense Department.

Dogs have 25 times more smell receptors than humans, Pitt said.

``We smell spaghetti sauce and we think, `Oh, the spaghetti sauce smells good,''' Pitt said. ``To a dog, they would smell the tomatoes, the onions, the basil, oregano. They smell all the odors individually.''

Insurgents have long stuffed roadside bombs into the carcasses of animals. But Iraqi security officials say they increasingly worry about the use of live animals.

``Dogs have been used in many areas by insurgents throughout Iraq'' to carry explosive devices, said Noori Noori, inspector-general at the Interior Ministry. ``They used mentally retarded people for operations during the elections, so why wouldn't they use animals?''

Last year in Ramadi, in the vast desert west of the capital, insurgents dispatched a booby-trapped donkey toward a US-run checkpoint around sunset. ``As one of the soldiers tried to stop it, the donkey exploded,'' said resident Mohammed Yas, 45. The only casualty was the donkey.

``Before, they used to use car bombs. Now they are using people and animals,'' said Colonel Adnan Jaboori, a spokesman for the interior minister. ``They are finding new ways to use remote-control technology.''

The daily newspaper Al Mada recently published an editorial cartoon showing an insurgent who strongly resembled Saddam Hussein trying to persuade a dog to strap on a belt bomb to advance the cause of the Baath Party, which once ruled Iraq. ``It is such a simple task,'' the insurgent tells the terrified dog. ``All you have to do is to put on this explosives belt, repeat the party's slogans, and may Allah have mercy on your father's soul!''