Senator Barack Obama won a commanding victory in the North Carolina primary on Tuesday and lost narrowly to Senator Hillary Rodham Clinton in Indiana, an outcome that injected a boost of momentum to Mr. Obama’s candidacy as the Democratic nominating contest entered its final month.

The results from the two primaries, the largest remaining Democratic ones, assured that Mr. Obama would widen his lead in pledged delegates over Mrs. Clinton, providing him with new ammunition as he seeks to persuade Democratic leaders to coalesce around his campaign. He also increased his lead in the popular vote in winning North Carolina by more than 200,000 votes.

“Don’t ever forget that we have a choice in this country,” Mr. Obama said in an address in Raleigh, N.C., that carried the unity themes of a convention speech. “We can choose not to be divided; that we can choose not to be afraid; that we can still choose this moment to finally come together and solve the problems we’ve talked about all those other years in all those other elections.”

In winning North Carolina by 14 percentage points, Mr. Obama  whose campaign had been embattled by controversy over the incendiary remarks of his former pastor  recorded his first primary victory in nearly two months. His campaign was preparing to open a new front in his battle with Mrs. Clinton, intensifying the argument to uncommitted Democratic superdelegates that he weathered a storm and that the time was dawning for the party to concentrate on the general election.