ASHINGTON
It is often said that war is too important to be left to the generals. But what about the C.E.O.'s? The Pentagon's plan to hire a private paramilitary force to guard sites in Iraq may have surprised many Americans, but it was really just another example of a remarkable recent development in warfare: the rise of a global trade in hired military services.

Known as "privatized military firms," these companies are the corporate evolution of old-fashioned mercenaries — that is, they provide the service side of war rather than weapons. They range from small consulting firms that offer the advice of retired generals to transnational corporations that lease out battalions of commandoes. There are hundreds of them, with a global revenue of more than $100 billion a year, operating in at least 50 countries.

Even the world's most dominant military has increasingly become reliant on them. From 1994 to 2002, the Pentagon entered into more than 3,000 contracts with private military firms. Companies like Halliburton, Vice President Dick Cheney's former employer, now provide the logistics for every major American military deployment. Corporations have even taken over much of military training and recruiting, including the Reserve Officer Training Corps programs at more than 200 American universities. (Yes, private employees now train our military leaders of tomorrow.)

Perhaps nothing better illustrates the industry's growing role than the campaign against Iraq. Private employees worked on everything from feeding and housing coalition troops to maintaining weapons systems like the B-2 bomber. Indeed, there was roughly one private military worker in the region for every 10 soldiers fighting the war (as opposed to one for every 100 troops in the 1991 gulf war).

And companies will play an even greater role in the occupation. In addition to the proposed security force, the new Iraqi military will be trained by corporate consultants. Washington has also contracted DynCorp, whose pilots have long helped the Pentagon destroy coca fields in Colombia, to train the new police force.

In many cases, privatizing war has allowed for greater military capacities and cost efficiency. A problem, however, is that while the industry has developed at a breakneck pace, governments and global bodies have responded at a bureaucratic crawl. There are almost no international laws or national regulations that have significant bearing on the industry.

This mix of profit motive with the fog of war raises several concerns. First, the good of private companies may not always be to the public good. All the normal worries one has with contractors (overcharging, overbilling hours, poorly trained workers, quality assurance) raise their ugly head; but in this case one is not dealing with a new plumber — lives are at stake. For example, a former DynCorp employee has accused the company of cutting costs by hiring former waiters and security guards to work as mechanics on Army helicopters.

Second, just like lawyers, some military contractors work only for ethical clients while others choose to make money from less savory types. As a result, some companies have helped save democratic regimes and aided humanitarian groups while others have supported dictators, rebel groups, drug cartels and terrorists.

In addition, foreign and military affairs are the government's domain. Undertaking public policy through private means can mean that some initiatives that might not pass public approval — such as the increasing American involvement, outside Congressional oversight, in Colombia's civil strife — still get carried out.

Also, privatized operations do not always go as planned. In 1998 the Colombian Air Force, working from intelligence supplied by an American company, mistakenly bombed a village, killing 17. In 2001 a plane carrying missionaries was shot down over Peru after private workers under contract to the Central Intelligence Agency alerted the Peruvian military that the plane seemed suspicious.

International and national laws must be updated so that governments gain some control over whom military firms are allowed to work with and can be certain the companies can be held accountable when things go wrong. Likewise, as governments come to rely more on private help, they must become more business-savvy, establishing good competition and oversight in their outsourcing. This is the only way to ensure that the public, not just the industry, enjoys the benefits of military privatization.

P.W. Singer is a fellow at the Brookings Institution and author of "Corporate Warriors: The Rise of the Privatized Military Industry."