DENVER — Senator Obama, standing where no black has ever stood before, swept to the Democratic presidential nomination on today as thousands of national convention delegates cheered his improbable triumph.

Senator Clinton asked the convention delegates to make it unanimous, the culmination of a painstaking agreement worked out between the two camps to present a unified front.

Mr. Obama was across town as the delegates he won in the primaries of winter and spring sealed his victory. Aides left open the possibility that he would briefly visit the Pepsi Center to thank his supporters, a routine event at recent national conventions. His formal acceptance speech tomorrow night was expected to draw a crowd of 75,000 at a nearby football stadium where an elaborate backdrop was under construction.

Mr. Obama, 47 and in his first Senate term, carries the Democrats’ hopes of recapturing the White House into the fall campaign against Senator McCain and the Republicans.

Inside the convention hall, the outcome of the traditional roll call of the states was never in doubt, only its mechanics.

“No matter whwere we stood at the beginning of this campaign, Democrats stand together today,” declared Rep. Debbie Wasserman Schultz, Democrat of Florida, a former Clinton supporter who delivered a nominating speech for Mr. Obama.

“We believe passionately in Barack Obama’s message of changing the direction of our country,” she said.

Earlier in the day, Mrs. Clinton formally released her delegates amid shouts of “no,” by disappointed supporters. “She doesn’t have the right to release us,” a Massachusetts delegate, Nancy Saboori, said. “We’re not little kids to be told what to do in a half-hour.”