The resignation of Agriculture Secretary Ann M. Veneman, the first woman to hold the post, caught many in the farm community by surprise yesterday.

Veneman had campaigned tirelessly for President Bush in key farm states in the run-up to the recent election. At a teleconference with reporters last Tuesday, she sidestepped a question about her future, saying only that "the president will be making decisions on personnel."

But in a letter to Bush just three days later, she declared that "now is an appropriate time for me to move on to new opportunities." The decision, said USDA spokeswoman Alisa Harrison, had been reached "in a private process between the secretary and the administration."

Among those mentioned yesterday as possible replacements were Allen Johnson, chief White House agricultural trade negotiator; Chuck Connor, agricultural adviser to the president; and two Texans with long service on the House Agriculture Committee, former congressman Larry Combest (R) and Rep. Charles W. Stenholm (D), who was defeated this month in a bid for a 14th House term.

Veneman's tenure spanned a tumultuous period that included the 2001 anthrax attacks, which revealed weaknesses in USDA agencies responsible for defending against bioterrorism; enactment of a new farm bill in 2002; major agricultural trade disputes with Europe, Asia and Brazil; and the first verified U.S. case of mad cow disease earlier this year.

In the midst of these challenges, in September 2002, Veneman announced that she was battling breast cancer.

James Webster, publisher of the biweekly Webster Agricultural Letter, called her departure "a real puzzle."

One clue to it, several sources said, may lie with proposals she made early in her tenure to reform the nation's costly farm subsidy system, which heavily benefits southern cotton and rice farmers and grain producers in the upper Midwest. Veneman is from California.

Congress largely ignored her proposals when it wrote the 2002 farm bill. But some in the White House reportedly felt that Veneman had been insensitive to the political impact of the initiative in farm states that would be crucial to Bush's reelection in 2004.

"She offended the big government wing of the Republican Party in the subsidized crop states," said Kenneth Cook, president of the Environmental Working Group. "They never trusted her after that."

Her departure, nonetheless, comes with the overall farm economy in good shape. USDA estimated last week that net farm income in 2004 will reach a record $77.5 billion, $9 billion more than last year.

Her work was applauded yesterday by a number of farm organizations with a business orientation, including the American Farm Bureau Federation. But she also received praise from several consumer and environmental organizations that seldom see eye to eye with Republican agriculture secretaries.

"Americans who care about food safety and nutrition will miss Agriculture Secretary Ann Veneman," said Carol Tucker Foreman, director of the Food Policy Institute at the Consumer Federation of America. "Veneman was always willing to meet with consumer representatives and hear our concerns."

Foreman, who was assistant secretary for food and consumer services in the Carter administration, said Veneman had defended rules requiring "zero tolerance" for E. coli bacteria in ground beef used in school lunches, and had urged the White House to release a proposed rule to control listeria, a cause of food poisoning.

However, Foreman and others have been sharply critical of the USDA's initial handling of the discovery of a cow infected with bovine spongiform encephalopathy (BSE) in Washington state this year, although no other cases have been reported.

Robert Vandermark, director of the forest program at National Environmental Trust, also faulted Veneman for not following through on a promise in 2001 to carry out a Clinton-era ban on road building in millions of acres of national forest and wilderness under the jurisdiction of USDA.

Farm and consumer groups hailed Ann Veneman's record, but others criticized her national forest policy.