Sen. Barack Obama began taking the first steps to unify the fractured Democratic Party for a general-election battle against Sen. John McCain, even as Sen. Hillary Rodham Clinton continued to insist that she has the backing of a broader coalition that could carry the party to victory in November.

Returning to Washington yesterday, Obama was mobbed by well-wishers as he walked onto the House floor. But behind the scenes, his campaign worked with a light touch to win over uncommitted superdelegates and allies of Clinton, mindful of not appearing overconfident and of the fact that they would need the backing of the candidate, her husband and their supporters in the fall.

With numerous prominent Democrats believed to be waiting in the wings to endorse his candidacy, Obama appears poised to win the pledged delegates and superdelegates he will need to claim the Democratic nomination as early as May 20, when Kentucky and Oregon vote. But although he appeared to lock down his lead on Tuesday with a strong win in North Carolina and a narrow loss in Indiana, he won only two new superdelegate endorsements yesterday, from Reps. Rick Larsen (Wash.) and Brad Miller (N.C.). Many other unaligned lawmakers said they are likely to remain on the sidelines for the time being, in deference to Clinton.

"Superdelegates understandably would prefer not to be seen as the deciding factor," Obama told reporters between meetings at the Capitol, brushing aside the suggestion that a mass endorsement is in the offing. "I think they respect the process, they respect Senator Clinton and myself."

As Clinton campaigned in West Virginia, which will hold its primary on Tuesday, her backers were also calling superdelegates, encouraging them to remain uncommitted until after the final two primaries on June 3 and touting poll numbers suggesting that Clinton would be a stronger nominee in key states such as Florida and Ohio. "Some people don't agree, but most people respect the argument," said Steve Grossman, a member of Clinton's national finance team.

In Charleston, W.Va., yesterday, Clinton argued that the coalition of voters backing her would make her more viable than Obama against McCain. "The delegate math may get complicated, but the electoral math is easy: We need 270 electoral votes to win in November," she said at a rally.

Clinton is expected to win the state by a hefty margin. Yesterday, she repeatedly referred to her appeal among "hardworking Americans," including "Catholic voters, Hispanic voters, blue-collar voters and seniors -- the kind of people who Senator McCain will be fighting for in the general election." She did not repeat the term "white voters," which she used in a USA Today interview published yesterday.

She also gave no hint of surrender in a letter to Obama about the delegate impasse involving Florida and Michigan. "Your commitment to the voters of these states must be clearly stated and your support for a fair and quick resolution must be clearly demonstrated," she wrote.

After Tuesday's primaries left Obama the clear Democratic front-runner, McCain's campaign refocused its attention on the senator from Illinois, preparing to question his experience on national security and his credentials on reform issues. Clinton, meanwhile, had become an afterthought for the presumptive GOP nominee.

"After I've been saying for a year, 'Don't count the Clintons out until they're out.' People are laughing at me," said Charles Black, a McCain campaign adviser. "I don't see how she does it."

Mark Salter, a senior McCain adviser, struck back sharply after Obama said on CNN that McCain was "losing his bearings" when he suggested that Hamas preferred that Obama be elected. Salter said Obama used the phrase "intentionally, a not particularly clever way of raising John McCain's age as an issue. This is typical of Obama's style of campaigning."

In Chicago, Obama's team worked to accelerate a transition to general-election mode that began weeks ago, only to be shelved as the primary showdown continued. In addition to competing in the six remaining contests, Obama will mix in stops to battleground states in the coming weeks, advisers said.

"We're not going to wake up in the morning after we become the nominee and be unprepared," said campaign manager David Plouffe.

The team is beginning two major grass-roots programs. "Vote for Change," a voter registration drive aimed at signing up millions of Democrats over the next six months, will begin tomorrow with 100 events in all 50 states. An army of "Organizing Fellows" is also being recruited -- full-time volunteers who will be deployed to swing states.

Obama spent the day in Washington courting uncommitted lawmakers. Former senator Thomas A. Daschle (S.D.), who helped organize the one-on-one and small-group sessions, said Obama is in striking distance of overtaking Clinton in superdelegate support, and may hit that mark in the next few days.

Obama's only public appearance was a lap around the House floor. He headed to a corner to visit Rep. John P. Murtha, the dean of the Pennsylvania delegation and a Clinton supporter, and Keystone State Reps. Mike Doyle, Paul E. Kanjorski, Jason Altmire and Robert A. Brady, all of whom are uncommitted.

Rep. Ellen O. Tauscher (Calif.), a Clinton supporter, waited her turn to shake Obama's hand, and uncommitted Rep. Bart Stupak (Mich.) chatted with the senator for a few minutes. House Majority Leader Steny H. Hoyer (Md.), also officially neutral, hugged Obama.

House Speaker Nancy Pelosi (Calif.) shrugged off the fuss, noting that "senators come to our floor all the time. Some attract more attention than others. I'm sure if Senator Clinton came, she would attract a great deal of attention, as well."

Obama advisers said a number of Democratic lawmakers are ready to sign on but want to speak with Clinton before making the leap.

"The writing is on the wall. They think he's the nominee, so there's no reason to rush," said one prominent uncommitted Democrat, referring to other lawmakers in the same situatin. "Then you don't have to offend anybody. The voters will issue their verdict soon enough."

Sen. Joseph R. Biden Jr. (Del.), a former presidential candidate, said he will remain neutral. "I'm hopeful that there's some accommodation pretty soon," he said carefully. "The sooner the better." Sen. Ken Salazar (Colo.) said he will hang back, as well. "Let it play out," he said. Sen. Mary Landrieu (La.) said she will continue to "contemplate things" over the next few weeks.

Clinton supporters also urged restraint. "It's three more weeks, okay?" said Sen. Maria Cantwell (Wash.). "We want to have a very united party in November, and I take Senator Obama at his word when he says he doesn't want to do anything to tell her to get out of the race."

Sen. Dianne Feinstein (Calif.) said she spoke with Clinton by phone for 15 minutes yesterday morning, with Clinton doing most of the talking and sounding "very collected" in her determination to stay in the race. "She doesn't believe it's time," Feinstein said, adding that Clinton feels a bond with those who have supported her and does not want to let them down.

Said Daschle: "We're not going to pressure her in any way." If superdelegates express concerns about offending Clinton, "we respect those," he said, adding: "I don't know that anyone is getting any pressure to come forward."