Denver — Senator Edward M. Kennedy, who is undergoing treatment for a malignant brain tumor, made a rare public appearance at the Democratic National Convention last night to support the party’s presumed nominee, Barack Obama.

Mr. Kennedy, a long-time champion of higher education who is chairman of the Senate education committee, has been mostly absent from Congress since receiving his diagnosis in May. But the senator’s voice was as booming as ever last night, even as it cracked occasionally with emotion.

“It is so wonderful to be here and nothing is going to keep me away from this special gathering tonight,” he said from the podium at the Pepsi Center here.

Responding to critics who say that Mr. Obama overpromises, Senator Kennedy likened Mr. Obama’s idealism to that of another Kennedy. “When JFK thought of going to the moon, he didn’t say, ‘It’s too far to get there, we shouldn’t even try,’” he said.

“This November, the torch will be passed again to a new generation of Americans,” he concluded. “The work begins anew, the hope rises again, and the dream lives on.”

As he exited the stage, shaking hands and hugging friends, the song “Still the One” played over the loud speakers.