In their demonstrations across the country, some Hispanic immigrants have compared the Rev. Dr. Martin Luther King Jr.'s struggle to their own, singing "We Shall Overcome" and declaring a new civil rights movement to win citizenship for millions of illegal immigrants.

Civil rights stalwarts like the Rev. Jesse Jackson; Representative John Lewis, Democrat of Georgia; Julian Bond and the Rev. Joseph E. Lowery have hailed the recent protests as the natural progression of their movement in the 1960's.

But despite some sympathy for the nation's illegal immigrants, many black professionals, academics and blue-collar workers feel increasingly uneasy as they watch Hispanics flex their political muscle while assuming the mantle of a seminal black struggle for justice.

But blacks and immigrants have long had a history of uneasy relations in the United States.

W.E.B. DuBois, a founder of the N.A.A.C.P., and other prominent black leaders worried that immigrants would displace blacks in the workplace. Ronald Walters, director of the African-American Leadership Institute at the University of Maryland, said blacks cheered when the government restricted Asian immigration to the United States after World War I. And many Europeans who came to this country discriminated against blacks.

Blacks and Hispanics have also been allies. In the 1960's, Dr. King and Cesar Chavez, the Mexican-American farm labor leader, corresponded with each other. And when Mr. Chavez was jailed, Dr. King's widow, Coretta Scott King, visited him in jail, Mr. Walters said. In recent years, blacks and Hispanics have been influential partners in the Democratic Party

Mr. Walters said he understood those conflicting emotions, saying he feels torn himself because of his concerns about the competition between immigrants and low-skilled black men for jobs. In 2004, 72 percent of black male high school dropouts in their 20's were jobless, compared with 34 percent of white and 19 percent of Hispanic dropouts.

"I applaud them moving out of the shadows and into the light because of the human rights issues involved," Mr. Walters said of illegal immigrants. "I've given my entire life to issues of social justice as an activist and an academic. In that sense, I'm with them.

"But they also represent a powerful ingredient to the perpetuation of our struggle," he said.