Throughout its evolution from dirt road to grand thoroughfare, the one-mile stretch of Pennsylvania Avenue between the White House and Capitol Hill has been an artery of power in Washington.

While inaugural parades and protests are public displays of the street’s prominence, John Harwood and Gerald F. Seib’s new book “Pennsylvania Avenue: Profiles in Backroom Power,” focuses on the avenue’s less conspicuous players, providing a window into how the power game works outside the halls of government.

Today, the Pennsylvania Avenue power structure has fallen into disarray, making it increasingly difficult for lawmakers to get anything done, the veteran journalists said.

“For a complex set of reasons, it has become an avenue divided — divided by party, ideology, money, technology — so that even the best of intentions these days often produce the worst of results,” they write.

In “Profiles in Backroom Power,” Harwood and Seib, who worked together on the White House beat for The Wall Street Journal, share their insider knowledge in colorful, pithy profiles of some of the avenue’s most connected power brokers. They illustrate how these players — who range from fundraisers to policy advisers — have mastered the labyrinth.

They describe, for instance, how former White House Social Secretary Lea Berman managed to skirt China’s thorny human rights record during a luncheon honoring a Chinese delegation by making last-minute seating chart changes and using diplomatic savvy. And they tell how House Democratic Caucus Chairman Rahm Emanuel (Ill.) jumped on the chance to achieve Democratic control of the House in the 2006 midterm elections the minute news broke that then-Rep. Mark Foley (R-Fla.) had sent suggestive computer messages to former House pages.

Harwood and Seib explain today’s highly divided politics by going back four decades to reveal the practices of influence and advocacy that culminated in the combination of narrow ideology and partisanship they say is unique to the Bush administration.

“Polarization is not something that originated with George W. Bush,” said Harwood, now the chief Washington correspondent for CNBC and a political writer for The New York Times, in an interview. “That’s the world that George W. Bush walked into.”

The Founding Fathers would likely not find today’s political divisions shocking, the authors noted.

“American democracy was always going to have conflict that was to a greater or lesser degree difficult to reconcile,” Harwood said. Today’s fights are “tame compared to some conflicts in the past.”

In 1856, following a disagreement over slavery, Rep. Preston Brooks (S.C.) strode into the Senate chamber and beat Sen. Charles Sumner (Mass.) unconscious. And Jack Abramoff may be the ghost of a 19th-century lobbyist who lured in Members of Congress by offering forgiving terms at his Pennsylvania Avenue gambling house.

The authors resist the Washington bashing that can be common among pundits.

“Amid all the problems, there’s also a certain majesty to this place, and I feel fortunate to live in this country,” Harwood said at a Thursday reception.

They also avoid the cynicism that can creep into political commentary.

“I think people come here because by and large they want to do the right thing,” Seib, now a Wall Street Journal editor, said at the reception.

The book closes on a hopeful note with descriptions of those who are crossing party lines to ease the gridlock on Pennsylvania Avenue. The final profile recounts how Ken Mehlman, former Republican Party chairman, brought law-school classmate Sen. Barack Obama (D-Ill.) to lunch to introduce him to Robert Strauss, former chairman of the Democratic National Committee.

Ending partisanship has been a pillar of presidential hopeful Obama’s message of change, and a central component of other campaigns. It is a goal Harwood and Seib said is realistic, because nothing is intractable on Pennsylvania Avenue.

By explaining Washington, Seib said, “Profiles in Backroom Power” may be able to stop political divisions from getting in the way of people trying to do the right thing.

The authors will be discussing their new book at Politics and Prose Bookstore, 5015 Connecticut Ave. NW, at 7 p.m. Friday.