Former Indiana Rep. Lee Hamilton, the top Democrat on the Sept. 11 commission, backed Barack Obama Wednesday.

Not only does the endorsement give a shot in the arm to Obama's national security credentials -- something heavily questioned by both presumptive Republican nominee John McCain and Obama's Democratic rival Hillary Clinton -- but it also gives Obama a big voice in Indiana, which holds the third most primary delegates among the remaining primary contests.

Hamilton, who during a three-decade House career rose to be chairman of the Foreign Affairs and Intelligence committees, also was vice chairman of the Sept. 11 commission.

"Barack Obama has the best opportunity to create a new sense of national unity and to transcend divisions within this country, not by ignoring them or smoothing them over, but by working together with candor and civility to meet our challenges," Hamilton said in a statement released by Obama's campaign.

On Obama's foreign policy stance, Hamilton said: "He will work with our friends and allies. Obama will strengthen our ability to use all the tools of American power, and relentlessly promote the American values of freedom and justice for all people."

Obama praised Hamilton for his leadership on the 9/11 Commission and the Iraq Study Group.

"Few public servants have done more to advance American foreign policy or to serve the people of Indiana, and I look forward to drawing on his counsel in the months ahead," Obama said in a statement.

Hamilton is best known as the top Democrat on the panel that investigated the 9/11 terrorist attacks. He also was co-chairman of the Iraq Study Group, a bipartisan commission that assessed U.S. policy in Iraq.

Although Hamilton is not a Democratic superdelegate, his backing comes on the heels of several high-profile endorsements for Obama, who leads Sen. Hillary Rodham Clinton in delegates for the party's nomination. Sens. Bob Casey Jr. of Pennsylvania and Amy Klobuchar of Minnesota endorsed Obama in recent days.

Hamilton is the highest-profile Indiana Democrat to back Obama before the state's May 6 primary. Sen. Evan Bayh and the bulk of Indiana's Democratic Party leadership have campaigned actively for Clinton in a state where neither candidate is regarded as a natural front-runner.

Hamilton spent 34 years in Congress representing a southern Indiana district before retiring in 1999.

Hamilton now leads the Woodrow Wilson International Center for Scholars in Washington. In a speech there last year, written by a longtime aide to Hamilton, Obama warned Pakistan that he would use military force if necessary to root out terrorists.