Only hours before the House's 316-108 vote, Mr. Bush had vetoed the five-year measure, saying it was too expensive and gave too much money to wealthy farmers when farm incomes are high. The Senate then was expected to follow suit quickly.
Action stalled, however, after the discovery that Congress had omitted a 34-page section of the bill when lawmakers sent the massive measure to the White House. That means Mr. Bush vetoed a different bill from the one Congress passed, leaving leaders scrambling to figure out whether it could become law.
Democrats hoped to pass the entire bill, again, on Thursday under expedited rules usually reserved for unopposed legislation. Lawmakers also probably will have to pass an extension of the current farm law, which expires Friday.
"We will have to repass the whole thing, as will the Senate," said Rep. Louise Slaughter, D-N.Y. "We can't let the farm bill just die."
Republican leaders called for a farm bill do-over. The White House, almost gleefully, seized on the fumble and said the mix-up could give Congress time to fix the "bloated" bill.
"We are trying to understand the ramifications of this congressional farm bill foul-up. We haven't found a precedent for a congressional blunder of this magnitude," said Scott Stanzel, a White House spokesman. "It looks like it may be back to square one for them."
"In all likelihood, you have to redo this process," said Rep. Roy Blunt of Missouri, the No. 2 Republican and one of the 100 GOP lawmakers who broke with Mr. Bush in voting to override the veto. "I'd like to see a farm bill passed that no judge can say is not the farm bill."
The legislation includes election-year subsidies for farmers and food stamps for the poor - spending that lawmakers could promote when they are back in their districts over the Memorial Day weekend.
The veto was the 10th of Mr. Bush's presidency. Congress so far has overridden him once, on a water projects bill.
With Mr. Bush at record lows in the polls in the waning months of his term, it was fellow Republicans who joined with majority Democrats in rejecting the veto. GOP lawmakers are anxious about their own prospects less than six months from the Election Day.
About two-thirds of the bill would pay for nutrition programs such as food stamps; about $40 billion is for farm subsidies; and additional $30 billion would go to farmers to idle their land and to other environmental programs.
Congressional Republicans overwhelmingly abandoned Mr. Bush in voting to pass the bill last week, overlooking its cost amid public concern about the weak economy and high gas and grocery prices. Supporters praised the spending on food stamps and emergency food aid.
Before the problem with the bill was discovered, White House spokeswoman Dana Perino said the legislation could make the situation worse for struggling families.
"Members are going to have to think about how they will explain these votes back in their districts at a time when prices are on the rise," she said. "People are not going to want to see their taxes increase."
Mr. Bush said the legislation needlessly would expand government. He cited one new program in the bill that would pay more to corn growers and others if agriculture revenue were to drop significantly in the next five years. This program, he said, could add billions of dollars to the cost of the bill.
He added that minor cutbacks to subsidies for wealthy farmers were not sufficient.
"At a time when net farm income is projected to increase by more than $28 billion in 1 year, the American taxpayer should not be forced to subsidize that group of farmers who have adjusted gross incomes of up to $1.5 million," the president said in his veto message.
Wednesday's snag stemmed from an error made while printing the legislation on parchment before sending it to Mr. Bush.
Democratic Rep. Steny H. Hoyer of Maryland, the majority leader, said the section in question - which deals with trade and international food aid programs - was never printed. Indeed, the final, 628-page version of the bill jumps straight from "Title II" on conservation programs to "Title IV" on nutrition programs.
Democrats proposed bringing up and passing the missing section separately and sending that to Mr. Bush, thus allowing the entire measure to become law. But Republicans argued that might not be constitutional because the president actually vetoed a version that Congress never considered.
The underlying bill would make small cuts to direct payments, which are distributed to some farmers no matter how much they grow. It also would eliminate some payments to individuals with more than $750,000 in annual farm income - or married farmers who make more than $1.5 million.
Individuals who make more than $500,000 or couples who make more than $1 million jointly in nonfarm income also would not be eligible for subsidies.
Under current law, there is no income limit for farmers, and married couples who make less than one-fourth of their income from farming will not receive subsidies if their joint income exceeds $5 million.
The farm bill also would: