DES MOINES, Iowa (AP) – President-elect Barack Obama has selected former Iowa Gov. Tom Vilsack as agriculture secretary, according to Democratic sources familiar with the selection process.

Obama will announce the appointment of Vilsack on Wednesday, according to the sources, who spoke on the condition of anonymity because they were not authorized to discuss the selection before the announcement.

Vilsack will be the fourth former opponent of Obama in the 2008 Democratic primaries to join his new administration. Others include Vice President-elect Joe Biden, Sen. Hillary Rodham Clinton, who has been tapped for secretary of state, and New Mexico Gov. Bill Richardson, selected to head the Commerce Department.

Vilsack positioned himself in the presidential campaign as a Washington outsider with heartland appeal, but he dropped out after poor showings in early primaries. He endorsed Clinton and campaigned actively for her in the long primary campaign against Obama. After Obama defeated Clinton, Vilsack endorsed him. First elected governor in 1998, Vilsack, 56, carved out a reputation as a political centrist. He balanced Iowa’s budget and resisted raising taxes, but he was willing to spend money on such priorities as education and health.

He argued that pushing alternative energy sources is key to bolstering rural sections of the nation that are struggling economically and with vanishing populations.