Democrats Barack Obama and Hillary Clinton looked ahead on Wednesday to a long and bruising presidential battle, and Clinton said she loaned $5 million (2.55 million pounds) of her own money to the costly fight to keep pace.

Republican John McCain, still facing conservative opposition, promised to unite his party as his coast-to-coast "Super Tuesday" wins in key states put him on the verge of clinching the nomination and capping a stunning political comeback.

"I do hope that at some point we would calm down a little bit and see if there are areas that we can agree on for the good of the party," the Arizona senator told reporters in Phoenix before a speech on Thursday to a conference of conservative activists in Washington.

Obama and Clinton battled to a draw on "Super Tuesday," with Obama winning 13 states and Clinton eight, including the big prizes of California and New York. Their delegate tally was almost even, propelling the fight toward the next round of seven Democratic contests in the next six days.

Clinton tried to keep up with Obama's growing fundraising prowess - he raised about $32 million in January to her less than $14 million - by loaning her campaign $5 million of her own money late last month.

"I loaned it because I believe very strongly in this campaign," she told reporters at her headquarters in Arlington, Virginia, a state that votes next Tuesday.

"We had a great month fundraising in January, broke all records, but my opponent was able to raise more money and we intended to be competitive and we were and I think the results last night proved the wisdom of my investment," she said.

As a show of solidarity some Clinton staff members have volunteered to go without pay, a Clinton spokesman said.

The Obama campaign urged its supporters to match Clinton's injection of funds and had already raised some $5.6 million since the polls closed on Tuesday, according to the Obama Web site.

Both candidates tried to lower expectations for the next contests as they looked toward a protracted Democratic fight. The Clinton camp said Obama was the party establishment favourite, and Obama said the same of her.

"We've got many more rounds to fight and you know I think that Senator Clinton remains the favourite because of the enormous familiarity people have with her and the institutional support she has," Obama told reporters in Chicago.

"But you know we're turning out to be a scrappy little team," he said. "I think we are less of an underdog than we were two weeks ago."

The Democrats will square off in Louisiana, Nebraska and Washington on Saturday, Maine on Sunday, and Virginia, Maryland and the District of Columbia on Tuesday - turf that could favour Obama.

The contests in Nebraska, Washington and Maine are caucuses, a format where he has performed well so far in the race. Caucuses are public gatherings of voters where his strong organization and grass-roots backing can pay off.

Under Democratic Party rules, delegates are proportioned by results statewide and in individual congressional districts. This enables both candidates to roll up big delegate totals even in states they lose.

TEXAS IN MARCH

That increased the likelihood the hotly contested race could last well into March contests in Texas and Ohio, an April contest in Pennsylvania and perhaps all the way to the party convention in late August.

"As we go farther and farther into this, it is less and less likely that either side will be able to significantly amass a large delegate lead," Clinton spokesman Howard Wolfson said.

Various estimates put the Democratic race for pledged delegates in an essential deadlock, with each campaign claiming a slight edge. Clinton leads among "super-delegates," the elected officials and party insiders who can switch allegiance at will.

All three of the senators in the presidential race - Obama, Clinton and McCain - returned to Washington on Wednesday for a Senate vote on an economic stimulus package.

"We will unite the party behind our conservative principles and move forward to the general election in November," McCain told reporters in Phoenix, acknowledging conservative concerns about his past stances on immigration, tax cuts and other issues.

McCain, whose campaign was all but dead last summer, won nine states on Tuesday, including California and New York, giving him a huge haul of the convention delegates who select the party's presidential nominee.

Republican rivals Mitt Romney and Mike Huckabee vowed to fight on but could face questions about their viability. Romney won seven states and Huckabee five.

An MSNBC count gave McCain 720 delegates, Romney 256 and Huckabee 194, pulling McCain closer to the 1,191 needed to clinch the nomination.

McCain, a former Vietnam prisoner of war who lost the Republican primary race in 2000 to George W. Bush, dropped plans for a possible trip to an international security conference in Germany so he could focus on his campaign.

Romney, a former Massachusetts governor and wealthy venture capitalist who has spent at least $35 million of his own money on the race, has argued McCain lacks the conservative credentials to be the party nominee.

Romney also is scheduled to address the conference of conservative activists in Washington on Thursday, while Huckabee was to speak there on Saturday.