Mercenaries or “soldiers of fortune” have gotten a bad name through the centuries. Yet, many Americans were not aware of the extent of the Bush administration’s use of mercenaries in the war in Iraq until four contract security guards employed by Blackwater Security Consulting of North Carolina were killed and mutilated in March in Fallujah. They heard more about them this week as the investigation into abuses of Iraqi prisoners widened.

The United States has quietly built what amounts to a mercenary army to help with the war in Iraq. Its strength, estimated at 15,000 to 20,000, makes it third, after the United States and the British, as contributors to the “coalition of the willing.”

Two Knight-Ridder reporters have reported the wide use of “hired guns,” writing that “thousands of former special operations soldiers are working for an untold number of private security companies, making far more than Uncle Sam paid them.” But their report added that “there are big risks with the big paychecks.”

Many highly trained American soldiers found they could make up to $500 to $1,500 a day by signing on with the private security firms under contracts with the Pentagon or with contractors or subcontractors. The Knight-Ridder team reported that as this private army expanded, standards dropped. They quoted a former CIA operative, Jamie Smith, the first director of Blackwater Consulting and now chief executive officer of SOG International Risk, as telling them by e-mail from Afghan-istan: “Companies often take anyone who says they can shoot a gun and are willing to travel, so long as that person is not a criminal.”

Criminals, too, seem to have made it into the mercenary ranks. The New York Times, in a major survey of the privatization of the war, reported that four private guards who were killed in an attack in January were revealed to be former members of apartheid-era security forces in South Africa. One had admitted to crimes in an amnesty application.

Outsourcing the war has obvious advantages to the Bush administration. The privately paid operatives don’t count in the troop total, which the administration has been hoping to reduce as the November presidential election approaches. And the costs come out of the fees paid to contractors rather than from military appropriations.

But there’s a downside. Members of the private army are not subject to military control. They often lack the wide array of weapons available to regular troops. They may be less able to call in air or artillery support in a pinch. And, from a public point of view, they can always quit and go home when the going gets tough.

This wholesale privatization may be getting out of hand. The Pentagon should be running the whole show. If it needs more manpower, it should step up recruiting rather than hiring private fighters, many of whom come right out of the elite regular military units trained by the U.S. government.