President-elect Barack Obama's call for the largest public-works program since the 1950s is the kind of dramatic investment that's needed to turn the economy around.

If the money is to be spent effectively, however, Congress and lobbyists will need to go on a low-pork diet. And that's not in their nature.

Obama wants to spend a record amount of taxpayer dollars, perhaps as much as $700 billion, on roads, bridges, schools, sewers, mass transit, dams, and new energy projects. It's central to his plan to create 2.5 million jobs. In the past year, 1.9 million jobs have been lost nationally, including 533,000 last month alone.

The president-elect fleshed out his rebuilding program after meeting in Philadelphia last week with the nation's governors, who have a long list of infrastructure projects waiting for funding.

When appropriators in Congress and lobbyists hear about such a large spending program, they can't help salivate, thinking about all of the goodies they can bring back home to their constituents and clients. Obama acknowledged this tendency when he warned Sunday that his administration will evaluate projects based on their economic impact, not on politics.

If anyone knows the temptations of pork, it's the president-elect. As a senator from Illinois, Obama requested $932 million in "earmarks," including $8.5 million to build permanent barriers to prevent the dreaded Asian carp from reaching the Great Lakes. (The goal was to protect commercial fishing, you see.)

If a reformed Obama truly intends to police the kind of spending habits he previously indulged, taxpayers should wish him well. The problem with earmarks is not just their overall cost, but that they often divert money from urgently needed projects to others of questionable value.

In fiscal year 2006, individual lawmakers inserted 8,056 earmarks worth more than $8.5 billion in the federal transportation budget. More than $5.6 billion, or 15 percent of the Federal Highway Administration's budget, was spent on projects hidden from public scrutiny. The practice allows lawmakers to bypass the usual federal and state planning procedures, and helps to turn low-priority projects into ones that get done.

Sen. Tom Coburn (R., Okla.), who ordered this transportation study, said 30,000 structurally deficient bridges could have been repaired if Congress had spent its 2005 highway pork on maintenance instead.

Not all earmarks waste money; some fund projects that are badly needed. But when states have $136 billion worth of infrastructure projects "shovel ready," lawmakers shouldn't be trying to jump the line simply to bring home a little more bacon to their districts.

That will increase the likelihood that a crumbling bridge somewhere won't get needed repairs.