Feb. 11 (Bloomberg) -- Barack Obama is poised to build on his weekend victories with three more wins over Hillary Clinton tomorrow in Maryland, Virginia and Washington, D.C.

Obama packed arenas in Baltimore and College Park, Maryland, today while Clinton pursued voters in smaller settings across the region. Polls in all three jurisdictions show Illinois Senator Obama the favorite to win a majority of the 168 delegates at stake in the so-called Potomac primary.

``We are under no illusions this is going to be easy,'' Clinton spokesman Mo Elleithee said. ``These are three primaries where the Obama campaign has a significant advantage.''

Obama has momentum going into the race after winning contests in four states over the weekend -- Maine, Nebraska, Louisiana and Washington -- and having battled Clinton to at least a draw on Feb. 5 when 22 states held contests.

His campaign claims a narrow lead in pledged delegates to the Democratic National Convention in August. An unofficial estimate by the independent non-partisan Web site thegreenpapers.com shows Obama ahead of Clinton, a senator from New York, 925 delegates to 896. An Associated Press projection shows Clinton ahead with 1,136 delegates to 1,108 for Obama. The AP count includes Democratic office holders and party officials who aren't bound by results in primaries and caucuses.

A candidate needs 2,025 delegates to win the nomination. Complete voting results aren't finished in all the states where voting has taken place.

Republican Race

On the Republican side, Arizona Senator John McCain, 71, and former Arkansas Governor Mike Huckabee, 52, are spending most of their time in Virginia, where McCain leads in the polls.

McCain, who has been confronted by skepticism from some leaders of conservative groups, won endorsements from party leaders in the state including former Senator George Allen, who was campaign co-chairman for Fred Thompson, who abandoned his presidential bid in January.

He was endorsed today by former Florida Governor Jeb Bush, the brother of President George W. Bush, who called him a ``devoted conservative leader.''

Obama, 46, has broad support in Washington, D.C., the nation's capital, where the majority of voters are black and where he has been endorsed by Mayor Adrian Fenty.

Clinton, 60, hasn't conceded the city. She visited supporters at the National Council of Negro Women Building yesterday, and former President Bill Clinton spoke to congregations of predominantly black churches on Sunday.

Obama Lead

Obama also has a lead in Maryland, which has two of the constituencies -- wealthy suburbanites and a large African- American community -- that polls show have favored him. A Feb. 7-8 survey by Mason-Dixon Polling & Research, Inc. conducted for MSNBC and McClatchy newspapers showed him leading Clinton by 18 percentage points, with 10 percent of voters undecided.

Clinton is relying on Democratic Party institutional support in the state, including campaigning by Senator Barbara Mikulski and Governor Martin O'Malley to generate enthusiasm from women and the party establishment.

Any lift she gets from party surrogates in Maryland may be mitigated by a large turnout of black voters and those in the 18-to-25 age group, said Matthew Crenson, professor emeritus at Johns Hopkins University in Baltimore.

``The idea that there's an organization here that could control the votes is diminished by the huge number of new registrations,'' Crenson said.

Difficult Road

Virginia's primary is open, meaning any registered voter, regardless of party, can chose a candidate from either ticket. Independent and swing voters factor in the political strategies of both Obama and McCain.

Clinton's team says they expect her positions on health care and the economy to resonate with rural voters in the southern part of the state, African-Americans and military personnel in the central Chesapeake region, and women and government employees in northern Virginia's Washington suburbs.

The campaign expects to ``win our fair share of delegates'' in Virginia, Elleithee said.

Clinton has the backing of state party powerhouse Lionel Spruill, an African-American member of the state House of Delegates. On Feb. 9, Spruill made the rounds with former President Bill Clinton.

Health Care

On Feb. 5, Clinton also won an endorsement from the Democratic Committee in Wise County, a rural coal-mining area where the poverty rate is more than twice the national average.

``Health care is very important to this region,'' said Wise County Democratic Chairman Melanie B. Salyer.

Still, Obama holds the lead in state polls, and he has collected endorsements from the state's top elected officials, including Governor Tim Kaine and Senator Jim Webb. Both men invited Obama to campaign for them in Virginia when each ran for statewide office, Kaine in 2005 and Webb in 2006.

Inviting Obama to campaign in a southern state when he was a relative unknown outside his home state of Illinois ``was a calculated, poll-tested decision, not made casually,'' said Representative Bobby Scott, the only black member of Virginia's congressional delegation and an Obama supporter.

The Mason-Dixon poll showed Obama's support at 53 percent in Virginia with Clinton's at 37 percent.

The same survey showed McCain ahead among Republicans in Maryland and Virginia.

To contact the reporter on this story: Lorraine Woellert in Washington, at lwoellert@bloomberg.net.

Last Updated: February 11, 2008 17:12 EST