Transformation is a tricky business. The U.S. military is discovering that fact on a daily basis in Iraq. And closer to home, Defense Secretary Donald Rumsfeld is reckoning with the obstacles to his ambition of transforming the U.S. military for the 21st century.

Rumsfeld created a special Office of Force Transformation to foster acceptance of ideas that could alter the fundamentals of warfare. The transformationalists let themselves imagine bombers without pilots, ships without crews, networks of sensors and precision-guided weapons that could see and destroy an enemy who lived in caves. They were intriguing ideas, leveraging America's overwhelming edge in technology. The problem was that for a military hungry for money to up-armor its Humvees and maintain its reenlistment rates, some of these concepts haven't been very practical.

Rumsfeld's engine of change for transformation was meant to be a budget process known as the Quadrennial Defense Review, usually referred to by its initials, QDR. This four-year budget planning exercise was started in 1997 under President Bill Clinton. This year's installment was intended to provide a road map for Rumsfeld's ambitious plans. Pentagon aides spoke of it as Rumsfeld's legacy document -- one that would put his stamp on the Pentagon for a generation.

A hint of what Rumsfeld had in mind -- and the political hurdles that stood in the way -- came in a document called "Program Budget Decision 753," which leaked in January. It proposed shifting resources from several expensive Navy and Air Force programs to help pay for the ballooning cost of the Iraq war, which is being fought mostly by the Army and Marines. Worried Air Force and Navy partisans knew where to go for help. The day after the document leaked, members of Congress from affected districts were racing to save the very aircraft carriers and fighter jets Rumsfeld had proposed to cut. In the end, PBD 753 was shelved and the decisions were postponed.

Rumsfeld still had big ideas this summer. His aides say he hoped to organize a Pentagon summit in July of top uniformed and civilian leaders, dubbed "Key West II" after the 1948 meeting between Defense Secretary James Forrestal and the Joint Chiefs of Staff that altered the roles and missions of the services. But Key West II never happened. Meanwhile, Rumsfeld's new deputy, Gordon England, took over supervision of the QDR process and began applying his business management experience to the transformation agenda. According to the New York Times, England identified more than 150 separate questions, including such acute practical problems as balancing reserve and active-duty forces.

The transformationalists had a powerful intellectual weapon in a document that came to be known as "the quad chart." It was a standard matrix, graphing threats to the United States according to their likelihood and the nation's vulnerability. At the top right, the zone of greatest likelihood and vulnerability, were "catastrophic" threats such as a terrorist attack with weapons of mass destruction. At the bottom left, the area of least likelihood and vulnerability, was a "traditional" attack involving conventional air, sea and land forces or established nuclear forces.

The quad chart suggested that the imminent danger to America came from al Qaeda, not from a rising conventional nuclear power such as China. That obviously was more bad news for the services that would fight a war against China: the Navy and Air Force. You don't have to be a cynic to recognize that recent studies warning of the Chinese military threat are, in the code of Pentagon budget wars, arguments for more Navy and Air Force spending.

This process of tempering big revolutionary ideas into smaller evolutionary changes is part of how the Pentagon works. John Hamre, who helped direct the 1997 QDR as deputy defense secretary, recalls: "You start with a grand vision of the future and end up patching holes in the budget."

Rumsfeld met this week with his top military and civilian brass to begin hammering out final decisions on QDR issues. The betting in the Pentagon is that Rumsfeld will fight for a document that focuses on the basics of transformation -- quicker, more flexible forces that can fight an Iraq war and also would do a better job of putting that country back together after the war. He'll also push for personnel and budget changes that will focus more of the 2.2 million people in the U.S. military on the problems that are proving so difficult for the 140,000 troops in Iraq. Perhaps he will revisit the question of whether we need so many fighters, aircraft carriers and submarines. But don't look for unmanned bombers or captainless ships anytime soon.

Transformation is one of Rumsfeld's best ideas. It would be a shame if his laudable effort to modernize the military got chewed up by the grinding pressures of Iraq and the internecine wars between the services.

davidignatius@washpost.com