Democratic Sen. Edward M. Kennedy of Massachusetts will endorse Senate colleague Barack Obama for president, party officials confirmed Sunday.The endorsement will be announced Monday in Washington, said the officials, speaking on condition of anonymity because they were not authorized to speak for the record. An official close to the senator said the announcement will be made during an Obama campaign rally at American University, where he will be joined by Sen. Kennedy and his niece, Caroline Kennedy, who also has endorsed Obama.