Correction: An earlier version of this article incorrectly said that Rep. Charles B. Rangel (D-N.Y.) was the first chairman of the caucus. Rep. Charles Coles Diggs Jr., a Democrat who represented Michigan from 1955 to 1980, was the first chairman. Rangel was a founding member. This version has been corrected.

Forty years ago, the purpose of a caucus to represent African Americans in Congress seemed clear to its founders: to eradicate racism.

The 13 legislators who formed the Congressional Black Caucus in March 1971 saw themselves as representatives of black people all over the country. Theirs was a role akin to those of civil rights activists. Only they had the bully pulpit of the country’s most powerful legislative body.

The current caucus members , who marked the anniversary of its founding this week, have a mission that is more diffuse, a role that is harder to define and power that has been fully absorbed into the nation’s political system.

For one, the caucus has 43 members from urban and rural districts. It includes one Republican. A handful of its members have been elected from majority-white districts. Eight have faced ethics investigations in the past three years. One of its members is the third-most powerful House Democrat, and a former caucus member sits in the White House.

“There are challenges today that we did not have then,” said Rep. Emanuel Cleaver II (D-Mo.), who chairs the caucus and represents a district that is majority white. “We cannot at all times have all of the members in sync because of the differences we have in our constituencies. But most of the time when we vote our conscience, we end up voting in a bloc.”

The challenges faced by the modern CBC include forging a relationship with the White House. President Obama met Wednesday with its leadership team. The conversation was wide-ranging, according to a CBC spokeswoman, and focused on federal budget issues and the country’s long-term investment in poor communities.

In the past, CBC members — five of whom sat down for a roundtable interview with The Washington Post this week — have complained of a distant relationship, while also reinforcing their support for Obama.

“There is a strong pressure in the system of government that we have to make it difficult for a progressive to stay progressive in the system. That goes all the way up to the White House,” said Rep. John Conyers Jr. (D-Mich.), who said it will be harder to get Obama reelected than it was to elect him. “We have a database on candidate Barack Obama, and we have a database on President Barack Obama. . . . They don’t comport.”

The tension with the White House is part of what the caucus sees as its historic role of holding presidents accountable to an agenda that advances African Americans. Still, it creates an awkward tension as the caucus continues to celebrate the ascension of a former member to the White House.

“There is no healthy relationship where two people do not disagree,” Cleaver said. “It has surprised me that journalists become candidates for cardiac arrest when they see or hear an African American disagreeing with an African American. We would become inauthentic if we did not have disagreements with this president.”

It was a political fight with a president that helped to forge the caucus’s reputation 40 years ago. In 1971, it was thought odd that 13 black congressmen, who held seats on none of the powerful committees in Congress, would band together. So when the caucus asked to meet with President Richard M. Nixon, he refused.

In turn, caucus members protested at his State of the Union speech by standing to walk out of the chamber, Conyers said. The caucus made headlines and eventually got Nixon to sit down with its members, which helped establish its credibility.

“Our doctrine for the CBC back in 1971 was the recognition that we as the black members of Congress have neither permanent friends nor permanent enemies, but we do have permanent interests,” said Rep. Charles B. Rangel (D-N.Y.), a founding member of the caucus.

The CBC, which was founded along with black affinity groups in many professions, has been a support system for its members. In recent years, CBC members have been intensely loyal and defensive of those in its ranks who have faced ethics charges. Rangel, who was censured on the House floor last year, was supported by all but one member of the caucus.

Rep. Maxine Waters (D-Calif.) is also drawing support from some caucus members as she faces a stalled investigation into whether she improperly worked to secure federal aid for a bank in which her husband was a large investor. Waters has said she plans to mount a vigorous defense.

In anniversary celebrations, the caucus will highlight legislative markers that include: getting set-asides for minority-owned businesses written into federal law, establishing a federal holiday in honor of the Rev. Martin Luther King Jr. and getting Congress to pass sanctions against South Africa during apartheid.

“We do not suffer in silence. We work outside the box,” Waters said. “We use every strategy that is available to us.”

Over the years, they also fought for plum committee assignments. It was a source of agitation and a joke among CBC members in 1971 that Shirley Chisholm — the first black woman elected to Congress — was assigned to an agriculture committee. She was from Brooklyn. “There are no trees in Brooklyn,” she would say.

“We thought we should utilize our strength by trying to get black members of Congress into the entire structure of Congress,” said Louis Stokes, a CBC founder who retired from the House in 1999 and is now a lawyer in Ohio.

Stokes became the first black member of the Appropriations Committee. Chisholm was appointed to the Rules Committee, and Rangel was assigned a place on Ways and Means.

Jim E. Clyburn, the third-highest ranking Democrat in the House, said the modern caucus has to be “innovative.” Clyburn (S.C.) cited the CBC’s push to include a program in the $787 billion economic stimulus package directing dollars to communities where 20 percent of the population has been living below the poverty level for at least 30 years.

Other strategies regularly employed by the CBC make noise but do not change policy, said Andra Gillespie, a political scientist at Emory University who has studied the caucus and black politics. Each year, the CBC writes an alternative budget — one that receives little attention on Capitol Hill. And its legislative conference is as notable for its social gatherings as for its political science panels.

“The criticism of the CBC is that its work is largely symbolic,” she said. “But we still need the caucus. We still need people to figure out what it takes to reduce the unemployment gap between blacks and whites and to reduce the wealth gap. They are a voice.”