WASHINGTON — With a rebuke to President Clinton, Senator Kennedy offered his full-throated endorsement to Senator Obama here yesterday, saying the freshman Illinois senator had “lit a spark of hope amid the fierce urgency of now” as he bestowed upon him the coveted mantle of his family’s legacy.

Appearing at a packed and raucous rally at American University, Mr. Kennedy peppered a thundering, 20-minute speech with swipes at
President and Senator Clinton, though he did not mention them by name.

“With Barack Obama, we will turn the page on the old politics of misrepresentation and distortion,” Mr. Kennedy said. He stood on a stage alongside his son, Rep. Patrick Kennedy of Rhode Island, and his niece, Caroline Kennedy, the sole surviving child of President Kennedy who announced her endorsement of Mr. Obama on Sunday.

Mr. Kennedy compared Mr. Obama’s candidacy to that of John F. Kennedy in 1960, saying that his brother, too, “faced public criticism from the preceding Democratic president.”

“Harry Truman said we needed ‘someone with greater experience,’ and added: ‘May I urge you to be patient,'” the Massachusetts senator said. “And John Kennedy replied: ‘The world is changing. The old ways will not do. It is time for a new generation of leadership.'”

“And so it is with Barack Obama,” Mr. Kennedy said to cheers. “He has lit a spark of hope amid the fierce urgency of now.”

Both Mr. Obama and Mrs. Clinton had aggressively courted Mr. Kennedy, a respected senior statesman in the Democratic Party long known as the “liberal lion” of the Senate. Though close with the Clintons, Mr. Kennedy was said to be angered by the tone of their attacks on Mr. Obama in recent weeks and rebuffed their pleas to at least remain neutral in the race.

Mr. Kennedy pledged to campaign aggressively for Mr. Obama, and an aide to the candidate said he would travel to Arizona, New Mexico, and California later this week before returning to the northeast in the days leading up to “Super Tuesday” on February 5, when Mr. Kennedy’s home state of Massachusetts will be one of 22 states holding primaries.

In another blow to Mrs. Clinton, Mr. Obama also picked up the backing yesterday of the Nobel Prize-winning author Toni Morrison, who famously referred to Bill Clinton as “the first black president.”

In words and image, yesterday’s rally evoked a passing of the torch, with Mr. Kennedy hailing Mr. Obama as a once-in-a-generation leader who could inspire the nation in the same way his brother did decades ago.

The joint appearance in Washington drew thousands to American University, and Messrs. Kennedy and Obama ended up delivering their speeches twice — once to an estimated 4,000 people crowded into a gymnasium and then again outdoors to the hundreds of people who could not get in.

Mr. Kennedy praised both Mrs. Clinton and John Edwards, but his speech contained a point-bypoint rebuttal of several central arguments that the Clinton campaign has made against Mr. Obama.

He responded directly to Mrs. Clinton’s repeated reminder that America needs a president who is ready “on Day 1.”

“I know,” Mr. Kennedy said of Mr. Obama, “I know that he’s ready to be president on Day 1.” And he took aim at the Clinton campaign’s contention that Mr. Obama had been inconsistent in his opposition to the Iraq War after speaking out against an American invasion in 2002.

Mr. Kennedy said Mr. Obama had stood against the war when “so many others were silent or simply went along.” And, he added, “Let no one deny that truth.” Mr. Obama heaped praise on each of the Kennedys, saying he stood alongside them “with a great deal of humility.”

Linking the Kennedys to his own family’s struggle, he told of how his father had come to America from Kenya with a grant from the Kennedy Foundation and the help of the “young senator from Massachusetts at the time, John F. Kennedy.”

Mr. Kennedy’s endorsement of Mr. Obama met with a harsh response from the New York chapter of the National Organization for Women, which is supporting Senator Clinton and said in a statement yesterday that “women have just experienced the ultimate betrayal.”