Washington, Feb 6: Hillary Rodham Clinton and Barack Obama dug in for a extended battle for the Demoractic presidential nomination after splitting wins in the biggest primary day in US history.

Republican John McCain all but wrapped up his party's nomination, winning the most important primaries and building what could be an insurmountable lead in delegates.

Hillary won California and New York, the most populous of the 22-states that held contests on Super Tuesday, and maintains a lead in the all-important tally of delegates.

But Obama is close behind and, with wins in at least 13 states, has fresh momentum as the Democratic race moves into territory where he would seem to have an edge.

Either Hillary or Obama will likely face a formidable opponent in John McCain, whose cross-country victories on Tuesday seem to guarantee he will be the Republican candidate in the November presidential election.

McCain's independent streak has won him support across party lines and, more than most Republicans, allows him to distance himself from the unpopular presidency of George W Bush.

McCain's victories in California, New York and other major states dealt a crushing blow to his main rival, former Massachusetts governor Mitt Romney, and capped a remarkable comeback for a campaign that nearly unraveled last year.

"We've won some of the biggest states in the country," McCain told cheering supporters at a rally in Phoenix.

An underdog for months, he proclaimed himself the front-runner at last, and added. "I don't really mind it one bit."

In the competition that counted the most, the Arizona senator had 613 delegates, more than half the 1,191 needed for the nomination - and far ahead of his rivals.

Even so, Romney and Mike Huckabee, a former Arkansas governor, said they were staying in the race.

Huckabee, a Baptist preacher, won contests in the south, his appeal to Christians conservatives there undermining Romney's support.

Hillary had 845 delegates, to 765 for Obama, out of the 2,025 needed to secure victory at the party convention in August.

Clinton's advantage is partly due to her lead among so-called superdelegates, members of Congress and other party leaders who are not selected in primaries and caucuses - and who are also free to change their minds.