A broad Pentagon directive issued this week orders the U.S. military to be sure, the next time it goes to war, to prepare more thoroughly for picking up the pieces afterward.

More than a year in the making, the directive represents an ambitious attempt to bring about a fundamental, permanent widening in what U.S. troops are trained and equipped to do. Accustomed to focusing primarily on combat operations, U.S. forces under the new order must now give post-conflict stability operations similar priority, which means they must be ready in foreign countries to carry out such tasks as developing political institutions, establishing judicial systems and reviving economic activities.

"Stability operations are a core U.S. military mission that the Department of Defense shall be prepared to conduct and support," the directive says. "They shall be given priority comparable to combat operations and be explicitly addressed and integrated across all" Pentagon activities.

The revised policy follows widespread criticism that the Pentagon neglected to plan sufficiently for the aftermath of the 2003 Iraq invasion. Not only did conditions in the country turn out worse than anticipated -- in the form of a fierce insurgency and mammoth reconstruction challenges -- but early Pentagon hopes of being able to hand off a large share of responsibility to U.S. and foreign civilian organizations and to Iraqis proved overly optimistic.

As a result, the U.S. military in Iraq has been badly stressed to come up with the skills, equipment and troops to ensure security and begin rebuilding the country. The difficult experience has driven home the lesson that U.S. forces cannot always depend on others to step forward and help manage stability tasks.

"Many stability operations are best performed by indigenous, foreign or U.S. civilian professionals," the directive says, reflecting the Pentagon's sentiment still that it need not always lead in this area. "Nonetheless, U.S. military forces shall be prepared to perform all tasks necessary to establish or maintain order when civilians cannot do so."

The 11-page directive, signed Monday by acting Deputy Defense Secretary Gordon R. England, assigns long lists of specific responsibilities to the Pentagon's various civilian branches, military services and regional commands.

For instance, it instructs the Pentagon's undersecretary for personnel to develop methods for recruiting people for stability operations and to bolster instruction in foreign languages and cultures. It orders the undersecretary for intelligence to ensure that "suitable" information for stability operations is available. And it directs the undersecretary for policy to create a "stability operations center" and submit a semiannual report to the secretary of defense.

These and other measures appear to go a long way toward addressing shortfalls highlighted in a critical study last year of the Pentagon's approach to stability operations. The study, done by the Defense Science Board, a Pentagon advisory panel, concluded that though U.S. forces are good at winning conventional battles, they have tended to give short shrift to managing the aftermath.

One of the reasons for this, experts inside and outside the Pentagon said, has been the assumption among military planners that U.S. forces could win wars quickly, then withdraw from combat zones.

"In the 1990s, the talk, every time we were going to deploy something, was, 'What's the exit strategy?' " said Andrew F. Krepinevich, executive director of the Center for Strategic and Budgetary Assessments. The focus in war games, he recalled, was: "How do we get forces to places quickly? It was assumed they wouldn't be there long."

But the Iraq conflict has made clear that a rapid exit is not always possible. Warning that Iraq may not prove an exception, the Defense Science Board recommended that stability operations be made an explicit mission of the Defense Department and treated with the same seriousness as combat operations. That led Defense Secretary Donald H. Rumsfeld to order the directive, senior aides said.

Craig Fields, who co-chaired the study, expressed satisfaction yesterday with the directive, an unsigned draft of which was reported on last week in the New York Times. "It covers a lot of ground, and it's in the right direction," he said.

At the same time, Fields noted that the release of the directive is only the start of change. Acting on it, he predicted, will "take a lot of effort over a long time."

Some defense scholars have urged the Pentagon to create constabulary units and other specialized forces to handle stability operations, saying that such troops could be kept abroad longer and provide skills not easily developed in conventional troops. But military commanders have considered the idea impractical, and Pentagon officials involved in drafting the new directive rejected it.

"As we looked at that question," said Jeffrey "Jeb" Nadaner, the deputy assistant secretary for stability operations, "we felt it was better to have the skills across the force."

Nadaner said the biggest sticking point during drafting of the document came in deciding who should monitor compliance. One option still being given serious consideration as recently as a few months ago involved putting a large committee in charge. But that was ruled out as too cumbersome, and the job ultimately went to the Pentagon's policy office.

"The idea is to get information frequently and directly to the secretary of defense so he could track the progress of change," Nadaner said. "If it's going through a big committee, there could be a lot of processing and a lot of delay."

Asked how much instituting the directive will cost, Nadaner said: "It shouldn't cost a whole lot, in the sense that it's not about the procurement of major weapons systems, which generally are your most costly things. It's about reshaping a lot of current activities."