At the dedication of the Triborough Bridge in 1936, Franklin Roosevelt made an impassioned case for public works. There was a time when no one complained, he said, “that our schoolhouses were badly ventilated and lighted” or that “there were no playgrounds for children in crowded tenement areas.” But times had changed. “People are demanding up-to-date government in place of antiquated government,” he declared, “just as they are requiring and demanding Triborough Bridges in place of ancient ferries.”

The Triborough was built by Roosevelt’s Public Works Administration, or P.W.A., one of his “alphabet soup” agencies. The New Deal public works programs are mainly remembered for giving jobs to victims of the Great Depression, but as Robert D. Leighninger Jr. argues in his recent book “Long-Range Public Investment: The Forgotten Legacy of the New Deal,” they also transformed the American landscape and greatly improved the nation.

The story of the 1930s public works programs is timely again, because much of America is falling apart. The deadly collapse of a Minnesota highway bridge in August shined a light on the poor state of the nation’s bridges, many thousands of which are “structurally deficient” by federal standards. Georgia’s failure to build enough reservoirs has contributed to a water crisis that could cripple metropolitan Atlanta. We should be thinking today about replicating some of the successes of the Depression-era programs.

The P.W.A., the Works Progress Administration and the Civilian Conservation Corps were primarily undertaken to put people to work at a time when the unemployment rate approached 25 percent, and to restart a woeful economy. Forward-looking officials like Harry Hopkins, the relief administrator, and Secretary of Labor Frances Perkins argued, however, that public works should be directed to socially useful programs.

Not all of it was. But the vast majority were enormously valuable. Great institutions were built, including the Bay Bridge, the Hoover Dam and Washington’s National Airport--now named for Ronald Reagan, Mr. Leighninger notes, even though it is “a product of the type of ‘big government’ program that he spent most of his political career opposing.” The New Deal programs also built thousands of important buildings, many beautiful, including the Alameda County Courthouse in Oakland, the University of Texas Tower and a reconstructed French Market in New Orleans.

Some projects were high-profile--notably the great hydroelectric dams and the presidential retreat at Camp David--but many more focused on the unglamorous mechanics of modern living, like water mains, pump stations, and sewage treatment plants. The W.P.A. alone built 78,000 bridges and viaducts and improved 46,000 more. It constructed 572,000 miles of rural roads and 67,000 miles of urban streets. It also built or improved 39,000 schools, 2,500 hospitals and 12,800 playgrounds.

The Civilian Conservation Corps, Roosevelt’s favorite, sent hundreds of thousands of young people into the countryside. They landscaped, and made accessible, sites like the battlefields at Gettysburg and Appomattox, and cleared the way for Virginia’s Skyline Drive. Most of their time was spent on tree planting, flood control, soil erosion efforts and fire prevention.

The New Deal public works programs have largely faded into history. Most people who use their handiwork, like the millions who travel over the Triborough or visit San Antonio’s River Walk, are unaware of how they came to be built. People rarely think about viaducts or sewage lines.

It is a legacy, though, that is worth recalling. There is a reason we are reading about bridges collapsing, water systems being overburdened and other system failures--like the 2003 blackout, which left 50 million people in the Northeast and Canada without power. Physical capital investment as a percentage of gross domestic product, the measure of how much the nation is investing in itself, is dismally low today by historic standards--and the $600 billion-plus being directed to the Iraq War is not helping.

Investing in the nation’s buildings, transportation and overall mechanics has often been viewed as a Democratic issue, but that may be changing. With Georgia’s water supply drying up, Representative John Linder, a Republican who has made a career of bashing Washington, is calling for a national commission on water resources. And after the Minnesota bridge collapse, the Senate passed a bipartisan bill to establish a national commission on infrastructure.

The nation is unlikely to embark on public works programs like those launched during the Great Depression, unless there is another economic crisis of that scale. But Roosevelt’s basic idea--that the government should employ idle hands to upgrade the nation--should never have gone out of fashion. The next president will need to confront the nation’s disrepair. It should be an issue in the campaign right now.