Jen Psaki, an Obama spokeswoman, confirmed the endorsement by Hamilton, who served as co-chairman of blue-ribbon commissions that investigated the Sept. 11, 2001, attacks and advised President George W. Bush on the Iraq war, Reuters reported.

Hamilton is a former Indiana congressman and is widely respected in that state, which holds its Democratic primary contest on May 6. The next primary is in Pennsylvania, on April 22.

The endorsement from Hamilton, a onetime chairman of the House committee on foreign affairs, will help Obama fend off criticism from Clinton that he lacks foreign policy and national security experience.

Speaking in Philadelphia on Wednesday against the type of trade agreements struck by the Clinton and Bush administrations, Obama also won the endorsement of a local affiliate of the AFL-CIO labor federation, which supports Clinton. The National Union of Hospital and Health Care Employees announced its backing for Obama.