WASHINGTON — Sen. Barack Obama is poised to get the endorsement of the powerful Teamsters, the second major union endorsement for the Democratic front-runner in a week, union officials told The Associated Press on Wednesday.

Obama will meet with Teamster President James P. Hoffa in Austin, Texas, on Wednesday. The endorsement is expected to come soon thereafter, said the officials, speaking on condition of anonymity because of the planned formal announcement.

The Teamsters represent 1.4 million members.

Union support will be key in the Democratic primaries in the next few weeks, particularly in Ohio on March 4 and Pennsylvania on April 22. Ohio and Pennsylvania have some of the nation's largest number of union workers, with more than 15 percent of the work force unionized in Pennsylvania and just over 14 percent in Ohio.

The Democratic presidential contenders have lobbied hard for the Teamster endorsement because of the power the union wields through its fundraising for Democratic candidates and get-out-the-vote programs. The Teamsters gave more than $2.2 million to Democrats in federal races in 2004. They have given more than $24 million to Democratic election causes since 1989, according to the Center for Responsive Politics.

The endorsement from the Teamsters is Obama's fourth from organized labor in a week. The 65,000-member International Brotherhood of Boilermakers endorsed Obama on Wednesday, the 1.9-million member Service Employees International Union backed the Illinois senator last Friday, and the smaller United Food and Commercial Workers endorsed him last Thursday.

Rival Sen. Hillary Rodham Clinton by far has a larger number of unions in her corner with 12 endorsements from unions affiliated with the AFL-CIO — the nation's largest labor federation — and the United Farm Workers from the rival Change To Win labor federation.

But Obama also has one AFL-CIO union in his corner — the Transport Workers Union. He also has the backing of the independent National Weather Service Employees Organization. And with a Teamsters endorsement, he will have four Change To Win unions in his corner: the Teamsters, SEIU, the United Food and Commercial Workers and UNITE HERE, who gave Obama his first national endorsement from a union.