In today's WSJ: FORT IRWIN, Calif.—The 1st Infantry Division's 2nd Brigade is supposed to represent the Army's new model—small and nimble. Lt. Col. Jason Wolter, a battalion commander in the brigade, said, half joking, he would conduct overseas training missions this year with "just the uniform on my back." Yet, the brigade landed here at the National Training Center ready for a full ground-war assault: 58 Abrams Tanks, each weighing 68 tons, along with 115 of the 33-ton Bradley Fighting Vehicles, a clutch of Humvees and a small fleet of drones. The apparent contradiction illustrates the Army's dilemma. As it prepares for peacetime budget cuts, the Army must shrink. But Pentagon officials say reducing ground forces too much would leave the U.S. vulnerable to threats by such countries as North Korea or Iran. That means continuing to train with tanks, heavy weaponry and big formations—and, in the view of some military analysts, pulling the Army back to its roots and away from its promised future. For years, there have been calls to shrink the Army, focusing on smaller, more-expeditionary operations. Now, U.S. military officials say it is finally time to decide the right balance of size, strength and security. Military spending cuts of nearly $1 trillion are slated over the next nine years under current law. And with the winding down of operations in Afghanistan, the U.S. looks to end a decade of counterinsurgency fights that have achieved mixed results, at best, leaving Americans to question the value of long ground wars. The Army is seen by some military analysts as a force from a past age, when wars were decided by tanks and artillery and the U.S. had the luxury of weeks or months to transport men and materiel to war zones. Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey and Army Chief of Staff Gen. Ray Odierno, say they want to reorganize U.S. ground forces to focus on smaller units with greater lethal force, fewer casualties and faster deployment. The days of "Industrial-age big formations with months to set the theater" are "if not gone, are going," Gen Dempsey said. "The kind of threats we can anticipate are rapidly developing threats." These same military reformers, however, say the Army must be ready for a full range of operations—from training allies to humanitarian relief missions to counterinsurgency fights to old-fashioned tank battles. Congress spent the last decade asking if the Army was big enough to simultaneously fight two ground wars. Lawmakers now must decide what to spend on such immediate missions as cyberdefense, training, no-fly zones, naval amphibious operations—and how much to set aside for any future ground war. John Nagl, a retired Army Lt. Colonel who teaches at the Naval Academy, is among those who say the Army hasn't fully embraced new ways to fight and win wars without massive armored forces. Rows of armored combat vehicles at Bagram Airbase in Afghanistan earlier this year await shipment to the U.S. Most U.S. forces are set to depart Afghanistan by the end of 2014. The Army's "organizational culture continues to focus nearly exclusively on state-on-state wars," he said, not the type of conflict he believes the U.S. is more likely to face in the future. "They appear to be unwilling to make that next big step," Mr. Nagl said, toward reorganizing the Army for more work advising and training troops of allied nations, for example. Pressure on the Pentagon is building. The 2011 Budget Control Act, which mandated across-the-board cuts known as the sequester, will cap military spending at $589 billion when the law expires in 2021, roughly the spending level of 2007. Lawmakers in both parties criticize the automatic cuts but undoing them will be difficult. Military leaders and the Obama administration have pushed, unsuccessfully, for a so-called grand bargain, a combination of spending cuts and tax increases to both shrink defense cuts. The current spending reductions aren't as deep as the cuts after Vietnam or the breakup of the Soviet Union, said military officers, but they will land faster. Next year, for example, the Army must cut its spending by as much as $14 billion. The Army is the largest military branch and—with salary, pensions, health care and other costs rising much faster than inflation—the most expensive. A single soldier costs the Army an average of $531,427 a year when at war overseas and $118,368 when garrisoned. Already, the Army has agreed to cut 80,000 people from its active-duty force, from a post-cold-war high of 570,000 in 2011. Retired Adm. Gary Roughead, the former chief of Naval operations, recently proposed bringing the Army down to 290,000, a suggestion that angered many Army officers. Defense officials said the Army must shrink by an additional 100,000 soldiers if the across-the-board cuts remain, bringing the service to 390,000. Other branches of the U.S. military are more secure, according to defense analysts. China's rise has cemented the Navy's importance. The Marines, used in military crises and humanitarian disasters, have a protected mission. The Air Force has fighter jets, as well as lethal, unmanned drones that can strike without immediate risk to U.S. troops. "It is almost like the Army needs a therapist," said a senior Army official. "Go lie down in a dark room and think about what does the nation expect of me and how am I going to do that." In World War II, the Army deployed divisions of 20,000 men who made up a mass convoy of mechanized infantry, artillery, medics, quartermasters, drivers and cooks. Few countries can fight the U.S. on those terms, even now. During the Iraq war, the Army shifted focus from large divisions to the 3,500-person brigade. The idea was to make units more flexible. But even the brigade may be too big. In the past decade of war, Gen. Dempsey said, most U.S. casualties have struck the Army's nine-soldier squads, its smallest unit. Giving squads better communications equipment and weapons would allow the Army to reduce casualties, lower the number of troops needed and speed deployments. "I challenged the Army instead of looking at itself from the top down, look from bottom up," Gen. Dempsey said. Gen. Odierno, Gen. Dempsey's successor as Army chief of staff, said his vision of a new Army looks to preventing wars as much as fighting them. He has assigned units around the world to train local military forces. The goal is to improve security in trouble spots without a U.S. military intervention. So-called regionally aligned forces can be deployed quickly in a crisis. "Warfare is changing," Gen. Odierno said. But even so, the Army can't turn its back on traditional combat operations that require moving heavy armored forces over long distances, he said: "There are some conventional things we have to be prepared to do—North Korea, Iran. If we don't have the capability we lose our ability to deter." Todd Harrison, a defense budget expert at the nonpartisan Center for Strategic and Budgetary Assessments, said the Army must assess the role of tank battles, given the global advantage of U.S. air power.