PORTLAND, Ore.  Gov. Bill Richardson of New Mexico delivered a forceful endorsement of Senator Barack Obama for president on Friday, urging Democrats to unite behind his candidacy to move the nation beyond its racial and partisan divide.

“It is now time for a new generation of leadership to lead America forward,” Mr. Richardson said, speaking to thousands of supporters at a rally here. “Barack Obama will be a historic and a great president, who can bring us the change we so desperately need by bringing us together as a nation here at home and with our allies abroad.”

Mr. Richardson, who sought to become the nation’s first Hispanic president, dropped out of the Democratic race in January after finishing behind Mr. Obama and Senator Hillary Rodham Clinton in the opening contests of Iowa and New Hampshire. Since then, he had been aggressively courted by his former rivals, but he said Friday that he could no longer stand on the sidelines of his party’s nominating fight.

“My great affection and admiration for Senator Clinton and President Bill Clinton will never waver,” Mr. Richardson said. “It is time, however, for Democrats to stop fighting amongst ourselves and prepare for the tough fight we will have against John McCain in the fall.”