Washington: An invigorated Barack Obama was hoping to rout Democratic rival Hillary Clinton in three presidential primary battleson Tuesday. The former first lady all but conceded she would lose those races, but dismissed talk that her campaign was in trouble after a string of earlier defeats.

Obama seemed to be coasting into yesterday's contests in Washington, DC, Virginia and Maryland, after he overwhelmingly won five weekend contests.

He was expected to be supported by black Democrats, a bloc that has aided his wins in earlier matchups against Clinton.

Republican fray

On the Republican side, John McCain hoped to rebound with three wins on the way to his likely nomination after embarrassing losses to Mike Huckabee in weekend contests showed he still had much to do to convince the party's core conservative blocs that he is one of them.

The Arizona senator lost contests in Kansas and Louisiana during the weekend, but managed a narrow win in Washington state caucuses that Huckabee, the former Arkansas governor, is now challenging.

Polls showed Obama with double-digit leads in both Maryland and Virginia, where Governor Tim Kaine campaigned at his side. The Illinois senator was counting on big wins in the so-called Potomac primaries - named after the river touching all three places - to erase Clinton's slim delegate lead for an edge in a contest that could stretch to the Democrats' national convention in August.

"We need something new," the first-term senator told a huge rally of 17,000 people at the University of Maryland on Monday, dismissing the former first lady's suggestions that he is not tough enough for the rigours of the presidency.

"I may be skinny, but I'm tough," he said, drawing loud cheers.

Obama was travelling late yesterday to Wisconsin, which votes next week, along with Hawaii, where he grew up. Meanwhile, expecting losses yesterday, as well as in other primaries during February, Clinton prepared to fly to Texas, which holds its primary on March 4.

The New York senator is banking on strong showings in Texas and in Ohio, which vote the same day, to blunt Obama's momentum.

Working-class support

Clinton generally has done well in larger states. She looks to draw support from the large numbers of Latinos in Texas and lower-income, working-class voters in Ohio.

"I wouldn't be doing this if I didn't think I would be the best candidate," Clinton told reporters Monday as she campaigned near Baltimore. "So I'm going forward - every day, we get to make our case to the American people."

In hypothetical general election matchups, a new poll conducted after last week's Super Tuesday contests found Obama edging McCain, 48 per cent to 42 per cent, while Clinton and the Arizona senator were tied - 46 per cent for Clinton to 45 per cent for McCain.

Despite what the poll numbers suggest, Clinton's strategists argued that she would be the stronger competitor against McCain because she has weathered Republican attacks throughout her career in politics and public service.

In the Republican race, McCain challenged the notion that he is too much of a maverick for conservative Republicans as he picked up the endorsements of Gary Bauer, an evangelical anti-abortion leader, and former Florida Governor Jeb Bush, the brother of President George W. Bush.

"We're doing fine. We're doing fine," McCain, a former Navy aviator and Vietnam prisoner of war, told reporters in Annapolis, Maryland.

Potomac Primary different equations

- Voters in the US capital city had a rare chance yesterday to affect national politics. The District of Columbia has no voting representation in Congress, and the city's overwhelmingly Democratic tilt means presidential candidates rarely bother to campaign there in general elections.

- In the Democratic contests, 83 delegates are at stake in Virginia, 70 in Maryland and 15 in the District. The primaries are not winner-take-all, and the delegates will be divided between Hillary Clinton and Barack Obama based on how they do statewide and in individual congressional districts.

- In the Republican contests, 63 delegates are at stake in Virginia, 37 in Maryland and 19 in the District. The winner of each contest gets all of the delegates, which could allow front-runner John McCain to pull farther ahead of his last remaining rival Mike Huckabee.

- Blacks make up 57 per cent of the population in the District, 30 per cent in Maryland and 20 per cent in Virginia - above the national average of 13 per cent. Blacks have heavily favoured Obama, who would be the first black president, over Clinton in Democratic state contests so far.

- Voting was to end at 7 pm EST (2400 GMT) in Virginia and at 8 pm EST (0100 GMT today) in Maryland and the District. None of the primaries are open to independent voters.