By Paul Kane

DENVER, Aug. 27 -- Laying the groundwork for his legislative agenda should he win the presidency, Sen. Barack Obama has begun courting the most powerful woman in U.S. politics: House Speaker Nancy Pelosi (D-Calif.).

Pelosi, who is chairing the Democratic Party convention here, stands atop Congress with unquestioned power. Elected as the first female speaker in January 2007, she runs a tightly controlled House in which she sometimes overrules the initiatives of her Democratic chairmen and regularly denies Republicans the chance to offer amendments. Democratic leaders believe the strength of the Obama-Pelosi relationship could be critical in determining the successes -- or failures -- of an Obama White House.

"Once he's elected, he's going to have to spend a whole lot of time with the speaker. Nancy's influence is not going to be surpassed by any event or any person," said Rep. James P. Moran Jr. (D-Va.), an early Obama supporter and a Pelosi loyalist.

While they have met in person only a handful of times, Obama and Pelosi have begun engaging in semi-regular phone calls, and their top staff members have started back-channel talks, according to aides to both lawmakers.

Obama and his running mate, Sen. Joseph R. Biden Jr. (Del.), have also launched a charm offensive. Hours before Biden's selection became known, Obama's camp floated the news that Pelosi's choice, little-known Rep. Chet Edwards (Tex.), had been a finalist. And before he was formally introduced, Biden called Pelosi to talk about the campaign, then followed up the next day, after her appearance on NBC's "Meet the Press," to compliment her on how she handled energy questions, according to an aide familiar with the discussion.

Pelosi gave Obama what many insiders considered political cover in June by supporting anti-terrorism surveillance legislation that liberal activists opposed. An hour after her vote, Obama released a statement citing exactly the same rationale as the speaker for supporting the measure, allowing him to cast a muscular anti-terrorist pose.

In late July, despite weeks of opposition by Pelosi to domestic drilling, Obama declared that he would back more offshore oil production in exchange for broader legislation including alternative fuel sources. Pelosi then reversed course and agreed to allow votes next month on a package that is similar to what Obama supports.

Pelosi views this fall's elections as the second phase of an eight-year plan that she hopes will leave House Democrats in charge for almost "as far as the eye can see," strengthening her already tight grip on the chamber.

"I have in my brain an idea that Democrats are going to be in the majority for a while, so get used to it," she said in an interview, predicting approval under her watch of a broad progressive agenda including universal health care and the promotion of renewable energy. "It is going to be a time of positive, constructive change."

But recent history is littered with Democratic presidents who campaigned as outsiders -- as Obama is now -- and ended up in feuds with Democrats on Capitol Hill. Bill Clinton's 1994 health-care plan never even received committee votes from Democratic chairmen. Jimmy Carter was considered so weak that Sen. Edward M. Kennedy (Mass.) -- home-state friend of then-Speaker Thomas P. "Tip" O'Neill -- ran against him in the 1980 presidential primary.

Despite staying publicly neutral in this year's Democratic primary, Pelosi made several moves that infuriated supporters of Sen. Hillary Rodham Clinton (N.Y.) and served as the first steps in the nascent Obama-Pelosi bond. Pelosi condemned the possibility that superdelegates could hand the nomination to Clinton if she won fewer primary votes. And as the last states cast their ballots, she called on undeclared superdelegates to get off the sidelines and announce their choices.

Pelosi's foes warned that Obama, who has some close Senate allies, should not take the speaker lightly, a mistake made by many past opponents.

"She's the most effective woman I've ever seen, hands down," said Rep. Deborah Pryce (Ohio), a member of the 2006 GOP leadership team that surrendered the majority to Pelosi. Pryce said Republicans doubted her toughness and assumed that Pelosi, a San Francisco liberal, would stumble and drive a wedge between herself and moderate Democrats.

Pelosi has had her share of failures, including her inability to impose an Iraq withdrawal timeline on President Bush. After failing to override his veto of the timeline in May 2007, congressional approval ratings went into a downward spiral that has left Pelosi overseeing the most unpopular Congress in history. "We haven't been able to force an end to [the war], so people don't care about the process. They just want results," she said.

But congressional Democrats scored victories on domestic legislation this summer, including an extension of unemployment benefits and a higher education program benefiting returning war veterans. In many cases, House Democrats had the upper hand on Senate Democrats in crafting the victorious strategy. Those policy wins, along with three special-election victories for Democrats this past spring, have left Pelosi a popular figure in all ideological wings of her caucus. Her campaign stops this summer included conservative pockets such as northern Kentucky and Alabama.

Republicans off Capitol Hill grouse that the effort to brand Pelosi as politically toxic has flopped. At a late-July meeting with young House Republicans, former New York City mayor Rudolph W. Giuliani recounted the regular attacks he faced in the mid-1990s over his ties to then-House Speaker Newt Gingrich (R-Ga.). "We have to be more aggressive branding Nancy Pelosi as the face of the Democratic Party," Giuliani said, according to one attendee.

Other Republicans predict that her governance style is bound for failure. "She gets credit if it goes well, but when it doesn't, she will continue to be the one to take the hit and the blame," said Rep. Kevin McCarthy (R-Calif.), a former minority leader in the California legislature.

Pelosi said she has not given Republicans "any grist for the mill," avoiding the sort of mistakes that plagued Gingrich with the federal government shutdowns in 1995. The key to her success, she said, has been Democratic unity -- something that is sure to be tested even more next year should Obama win and Democrats pick up bigger majorities.

"We all grow stronger together. So it's not just about me being stronger," Pelosi said.