Four months later, Dingell (D-Mich.) appeared in the speaker's conference room to walk through a bill that would override California's attempts to combat global warming by raising fuel efficiency standards, strip the Environmental Protection Agency of its authority to regulate greenhouse gases and promote a controversial effort to turn coal into liquid fuel.

This time, Pelosi was in no mood to mollify Dingell. The bill he was sponsoring, she said, was unacceptable. The environmental costs would be too severe, the political costs for the Democratic caucus too high, she said.

The two episodes with Dingell illustrate Pelosi's evolution from a somewhat tentative political figure reliant on a small circle of advisers to the undisputed leader of the House's fractious Democratic majority.

"Nancy now represents the majority of this caucus, overwhelmingly," said Barney Frank (Mass.), chairman of the House Financial Services Committee.

But if Pelosi has succeeded in uniting her party during her initial months as speaker, she and the rest of the leadership have yet to convince the nation that the Democrats can govern.

Pelosi, of California, has succeeded in getting all of her opening agenda through the House. But few of the initiatives have made it to the president, and only one has become law: an increase in the minimum wage.

The obstacle has been the Senate, where Democrats hold only a one-seat advantage. But that failure has colored all of Congress, including Pelosi and the House Democratic leadership.

The new Democratic Congress took office in January with a 43 percent approval rating. Since then, its rating has sunk to about the same low levels as President Bush's, a bit below 30 percent. And Pelosi's own approval ratings have slipped, from 48 percent in a March poll by the Pew Research Center for the People and the Press to 36 percent last month in a Los Angeles Times/Bloomberg poll. Over the same time frame, her disapproval ratings climbed from 22 percent to 39 percent.

As the first speaker since Newt Gingrich (R-Ga.) to have to manage a new majority after a switch in party rule, Pelosi came in with an ambitious 100-hour agenda and some challenges that would quickly strain the Democratic caucus: finishing all of the government's domestic budget plans left undone by the Republicans, enacting an ethics program unpopular with many lawmakers and, most important, funding a war most Democrats oppose.

Pelosi faced an inherent conflict — unite a Democratic majority or fulfill her promises to run a more transparent and bipartisan House. In her first six months, she has chosen the former, not without a price.

Combative Republicans repeatedly tried to use her initial openness against her. They tried to force a vote to end the District's gun ban as a price for giving the city a vote in the House and attempted to make Democrats vote on a GOP resolution declaring that the House would always fund the troops in Iraq, at a time when many liberals wanted to end funding. In both instances, Pelosi pulled the proposals before they were voted on, violating her pledges of bipartisanship but keeping Democratic unity intact.

Now Democratic leaders worry that they must get some of the domestic agenda passed soon, to show voters they can govern, even as they are still dogged by a creative Republican resistance that has bedeviled Pelosi and her party.

After the 2006 elections swept the Republicans from power, Pelosi stood as a historic figure, the highest-ranking elected woman in the nation's history. But she had no obvious models on which to build her speakership.

The last time a Democrat took the gavel from a Republican speaker was 1955, when Sam Rayburn (Tex.) resumed a speakership he had relinquished only two years before. The most recent Democratic speakers — Thomas P. "Tip" O'Neill (Mass.), Jim Wright (Tex.) and Thomas S. Foley (Wash.) — reigned over a Democratic caucus that had grown complacent after decades in power. Those speakers passively allowed their powerful committee chairmen to set the legislative agenda.

Pelosi's situation made her most like Gingrich, another politically minded insurgent who assumed control after years in the minority. Like Gingrich, she rose not through the committee structure but by playing in the rougher world of politics.

Pelosi wanted to maintain the Republicans' much more centralized power structure but recognized that old bulls such as Dingell, David R. Obey (D-Wis.) and John Conyers Jr. (D-Mich.), who had served as committee chairmen before the GOP swept to power, would have to be respected.

"There is a necessity for a unity of voice and purpose in the Democratic Party . . . and the only way you're going to do that was to have a central management to create consensus, not simply individual, discrete committee agendas," said House Majority Leader Steny H. Hoyer (Md.).

But as the face of that central power, Pelosi, who declined an interview request for this article, lacked Gingrich's flair for public appearances and off-the-cuff prognostication. Her sex made her extraordinary, but it was also something of a liability, leading her to be constantly underestimated, said Steve Elmendorf, who was chief of staff to Richard A. Gephardt (Mo.) when he was House minority leader.

"We would have these private meetings when she was [House minority] leader where she was decisive, focused, even dismissive of people at times," Frank said. "I'd say to her, I'd beg her, 'Please, Nancy, be this person in public.' "

But to some Democrats, her biggest liability was the tight circle of confidants — tough-minded fellow Bay Area liberals such as Reps. George Miller, Anna G. Eshoo and Zoe Lofgren; tart-tongued Reps. Edward J. Markey (Mass.) and Rosa DeLauro (Conn.); and gruff Rep. John P. Murtha (Pa.) — that allies worried would insulate her from public opinion and the rest of the caucus.

Even before she received the gavel, those fears appeared to be confirmed when she disastrously backed Murtha's challenge to Hoyer for majority leader. She saw the Iraq war as the defining issue of the time and extolled Murtha as the man to end it, but he was trounced.

"That was a defining moment for her," said Rep. C.A. "Dutch" Ruppersberger (D-Md.), whose political roots are entangled with Pelosi's in Baltimore, where she grew up. "It made her stronger, because she understood then that she really had to widen her circle."

Once she assumed the speakership, Pelosi took on a frenetic schedule. She met with Democratic leaders formally three times a week but often informally two to three times daily, and held sessions with chairmen, freshmen and other lawmakers.

There is a downside to the pace. She tends to micromanage, frustrating staff members with her unwillingness to delegate tasks, and she jealously guards her schedule.

Still, an instinct for compromise and consultation got Pelosi through a series of initial tests that could have blown up publicly but instead passed quietly. After Murtha's defeat in November, his close ally Rep. James P. Moran Jr. (D-Va.) said lawmakers who had promised their votes to Murtha but delivered them to Hoyer were not to be trusted and should be unmasked. Brendan Daly, Pelosi's communications director, got wind that Moran would be on PBS's "NewsHour" and quickly called Moran's staff to command that he not go on the show and that he stop the threats.

Just weeks later, Pelosi pushed aside Jane Harman (Calif.), the highest-ranking Democrat on the intelligence committee, then skipped over Alcee L. Hastings (Fla.), an African American and an impeached federal judge who was next in line, to name Sylvestre Reyes (Tex.) as chairman of the powerful Permanent Select Committee on Intelligence. The move was expected to cause an uproar, not only with the Congressional Black Caucus but also with the "Blue Dog" Democrats — conservative and moderate lawmakers who backed Harman. It did not, however, because she has provided other key assignments to assuage those left out.

The next challenge came as House Democratic leaders tried to force a turn in the Iraq war through a spending bill, only to have Pelosi sideswiped by the man she had entrusted to end the war — Murtha.

Senior Democrats had been huddling with different factions of the caucus, trying to reach a strong consensus before going public with a bill. Without telling Pelosi, Murtha laid out the bill's strategy on a liberal Web site, MoveCongress.org. The legislation called for such stringent readiness standards for deploying combat forces that the president's planned troop increase would be strangled by red tape.

Pelosi learned of Murtha's remarks from reporters. At that point, authority over the war-funding bill very publicly shifted to the House Appropriations Committee and Obey, its chairman, who was conspicuously not a member of her inner circle.

"Murtha said, 'I had my plans.' He couldn't get them done, so Obey took over," said a senior House Democratic leadership aide, who spoke on the condition of anonymity because he was not cleared to discuss internal deliberations.

By the time Pelosi met with the chairmen last month to finalize the House's energy bill, her grasp on the levers of power was nearly complete. It was at this meeting that she shut down Dingell's proposals as harmful to the environment, and thus to her caucus. According to participants, she virtually manhandled Dingell, the House's longest-serving member and, at age 81, still an imposing figure.

Dingell grew angry, but he directed his rage not at Pelosi but at Caucus Chairman Rahm Emanuel (Ill.), who had tried to cool him down. If Emanuel wanted to get involved in energy policy, he should try to get on the committee, Dingell snapped.

Emanuel was happy to take the heat.

"I was never part of and still am not part of that Miller/Eshoo/Lofgren/Murtha circle," Emanuel said, "and I would consider myself a true Pelosi loyalist."

To be sure, the inner circle remains powerful, particularly Miller. His longtime chief of staff, John Lawrence, is now Pelosi's chief of staff. Another veteran Miller aide, Dan Beard, is the House's new chief administrative officer, responsible for everything from broken BlackBerrys to the Capitol's decrepit power plant.

But even Pelosi's closest confidants say their influence has been diluted by the demands of the speakership. Eshoo grew wistful as she spoke recently of her "pal" Pelosi.