Through the 1980s, the Democrats struggled over abortion. But by the 1990s, the share of Americans supportive of abortion rights had grown. Democrats lost their majorities for 12 years, leaving the most liberal and pro-abortion rights members in office. As a result it seemed to fade as a public issue. Now, however, Democrats once again have a large and diverse House majority, with more members from conservative-leaning districts where anti-abortion rights groups are active.

It was that division that played out behind the scenes late last week, and into the weekend, and came powerfully in the open as the issue.

Earlier Friday, Ms. Pelosi and her supporters thought they had a deal that would quiet the fight between abortion foes. Representative Bart Stupak, Democrat of Michigan, an anti-abortion leader, said he thought so, too  until, that is, Ms. Pelosi called to tell him it was dead.

“We had an agreement at 7:30, 8 o’clock,” said Mr. Stupak, who added that he had called nearly 40 other lawmakers favoring tighter abortion restrictions to make sure they would back the deal. But then Ms. Pelosi called. “The deal’s off,” he quoted her as saying. “It’s not my choice. I can’t hold my side together.”

The sensitivity around the abortion fight  and the likelihood that it would not disappear from the health care debate  was evident from the start of floor proceedings on the health care bill on Saturday.

And it was part of the drama outside the Capitol as well. Roughly 300 protesters who rallied against the health care bill included a number of anti-abortion demonstrators with large placards showing grisly photos identified as aborted fetuses. Inside the building, House Democratic leaders had hoped to spend the day rallying their members around a historic vote. President Obama, visiting the Capitol to make a personal appeal to lawmakers, likened the bill to two of the party’s greatest achievements: Social Security under Franklin D. Roosevelt and Medicare under Lyndon B. Johnson.

Instead, Ms. Pelosi found her caucus still caught up in the fierce dispute over abortion.

On Friday, Ms. Pelosi met twice with Democratic lawmakers from the Pro-Choice Caucus. In between, she huddled with staff members from the bishops conference, Mr. Stupak and two other leading Roman Catholic lawmakers, Representative Mike Doyle, Democrat of Pennsylvania, and Representative Brad Ellsworth, Democrat of Indiana.