A speech delivered by a Black Muslim leader at last week's March on Washington II--in which he proclaimed a willingness to work in partnership with other groups, including whites--is being praised as perhaps the most significant and stirring of the day, according to march organizers and participants.

The speech, little noticed by the media but a crowd pleaser at the Lincoln Memorial rally, was made by Minister Louis Farrakhan, the Chicago-based leader of the Nation of Islam. Farrakhan's group is an offshoot of the Black Muslim separatist group once led by Elijah Muhammad and popularized by Malcolm X, a group that boycotted the original 1963 civil rights march.

"Every black man, woman and child in this country, indeed, every black person on the earth, has benefited from the civil rights movement and the leadership of Dr. Martin Luther King Jr. and all of the martyrs that shed their blood to make his dream a reality," Farrakhan told marchers, explaining his decision to appear at the 20th anniversary gathering.

His speech, while not new in its conciliatory tone, was the most public declaration to date that Black Muslims are willing to join forces with other groups, irrespective of race and religion, to work for social and political change.

"No longer can we be separate, you there and me here or me here and you there," said Farrakhan, who spoke late in the afternoon. "You Muslim, you Christian, you Baptist, you Catholic, we cannot tolerate any longer these artificial barriers that divide us as a people." He said he had come to the rally to "lift up my voice" in protest with "Christians and Jews and Muslims and agnostics and atheists and black men and white men and brown men and yellow men and women."

Even before the death in 1975 of Elijah Muhammad, according to Black Muslim spokesmen and those familiar with Islamic religious teachings, the group had been moving away from much of its anti-white rhetoric. The willingness to work with other races and religions has continued in recent years, even after the group split into two rival factions--the Nation of Islam headed by Farrakhan and the American Muslim Mission led by Elijah Muhammad's son, Imam Warith-Deen Muhammad--each claiming to be the true successor to the original Muslim religion for American blacks.

According to march organizers, representatives of both groups were invited to address last Saturday's "Jobs, Peace and Freedom" rally, but only Farrakhan agreed to participate.

The 50-year-old Nation of Islam leader's speech was noticeable also in that it did not directly attack President Reagan, as did many of the 40 other rally speakers, but instead leveled a blistering attack on American society and overall government policies.

"A nation's greatness is measured by its ability to give justice to the poor, the oppressed, the weak, the disadvantaged," said Farrakhan, who argued that the country had prospered on the "sweat and blood" of black slaves, American Indians, Mexican Americans and other "people of color."

To live out the American creed that all people are created equal, Farrakhan said, the U.S. government "must overcome this propensity toward racism" and "stop the wanton murder of black men, women and children in the ghettos of America by brutal police force."

The nation must also, he said, "overcome this desire to move into foreign countries and dictate who will be their leader and what kind of government those people shall have. . . . This government must say that it will overcome the desire to tell others how to live abroad while neglecting Americans at home."

Farrakhan could not be reached to discuss his appearance at the march, and a spokesman for him said the Black Muslim leader does not give interviews.