WRAPUP 10-Obama moves closer to US presidential nomination

* Obama wins Oregon, claims milestone

* Clinton takes Kentucky, vows to fight on

* Obama raises $31 million in April (Recasts with Oregon, details)

By John Whitesides, Political Correspondent

WASHINGTON, May 20 (Reuters) - Barack Obama passed a major milestone to move within reach of the U.S. Democratic presidential nomination on Tuesday, but rival Hillary Clinton refused to surrender.

The pair split two nominating contests, with Obama handily winning Oregon and Clinton crushing the front-runner in Kentucky, to give Obama a majority of pledged delegates won during their lengthy state-by-state nominating fight.

Obama hoped the milestone marked the beginning of the end of the grueling battle, and he turned his attention to a general election matchup with Republican John McCain in November.

"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 a rally in Iowa, site of his breakthrough victory in the first Democratic contest on Jan. 3.

The Illinois senator returned to the theme of change that propelled him to the front of the Democratic race during the early contests. He described the battle with McCain as "more of the same versus change. It is the past versus the future."

But Clinton gave no sign she was ready to quit, 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.

"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 after Tuesday's votes are counted, Obama will still be about 70 delegates short of the 2,026 needed to win the nomination at the Democratic convention in August.

But he hopes the pledged-delegate milestone will push more undecided superdelegates -- party officials who can back any candidate -- his way.

Obama 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 against McCain, an Arizona senator. Her victories in big states like Pennsylvania and Ohio gave her a broader base of support than Obama, she said.