Democrat Barack Obama won a US presidential nominating contest in Oregon, NBC News projected, while rival Hillary Clinton cruised to a rout of the front-runner in Kentucky.

The results gave Obama a majority of pledged delegates won in the lengthy state-by-state nominating fight with Clinton.

He hopes that milestone marks the beginning of the end of their gruelling Democratic race for the right to face Republican John McCain in November's election.

"We have returned to Iowa with a majority of delegates elected by the American people and you have put us within reach of the Democratic nomination for president of the United States," Obama told supporters in Iowa, site of his breakthrough win in the first Democratic contest on January 3.

At a rally outside the Iowa state capitol in Des Moines, the Illinois senator turned his attention to a showdown with McCain and said their November battle would represent "more of the same versus change. It is the past versus the future."

But Clinton gave no sign of surrender, promising supporters in Kentucky that she would keep fighting until the Democratic voting ends on June 3.

"I'm going to keep making our case until we have a nominee - whoever she may be," said Clinton, who has shrugged off calls to drop out of the race for weeks.

"We have to select a nominee who is best positioned to win in November and someone who is best prepared to address the enormous challenges in these difficult times," the New York senator and former first lady told supporters in Louisville.

Even with Tuesday's results, Obama will still be about 50 delegates short of the 2,026 needed to win the nomination at the Democratic convention in August. But he hopes the milestone will start more undecided superdelegates - party officials who can back any candidate - flooding his way.

He contends those superdelegates, who have been breaking his way heavily in recent weeks, should support him because he won the most delegates in state voting.

Clinton says they should reconsider because she would be a stronger opponent for McCain, an Arizona senator. Her victories in big states like Pennsylvania and Ohio gave her a broader base of support than Obama, she said.

Reuters