The country's leading black congresswoman last week called on affluent blacks to shake off their lethargy and fight to preserve what blacks have gained over the last 20 years.

Speaking to the Montgomery County Alumnae Chapter of Delta Sigma Theta sorority, an organization of professional black women, Rep. Shirley Chisholm (D-N.Y.) said blacks must shake off the "Rip Van Winkle syndrome" and "recognize that in order to get change, we have to move."

The Montgomery Chapter of Delta Sigma Theta is composed of professional, college-educated black women and has about 220 members. It describes itself as a public service organization; it raises money for education loans and scholarships, and encourages political participation. Chisholm is a member of the organization.

She said that blacks today face the greatest challenge of recent years and that "blacks are suffering disproportionately, much more than other groups in this country," under President Reagan's administration.

She noted that unemployment is highest among young blacks, but added that even blacks who had held high-paying jobs are out of work. They are victims, she said, of the "last hired, first fired syndrome."

Affirmative action programs, basic civil rights and voting rights are all under attack, she said, adding that Reagan's policy of handing over more power to local jurisdictions is dangerous for blacks.

"The reason for so many years we have had to have the intrusion of the federal government into the lives of the people was precisely because we could not depend on those who were delegated the authority," she said. "If we had depended on the states, who knows? We may not have had voting rights, civil rights legislation. We cannot depend on the morality of those who are in authority at the local level."

Chisholm, who said she will not run for reelection this fall, said she will nevertheless fight to preserve what blacks have attained.

"I will be fighting, I will be marching, I will be organizing," she said. She would not elaborate on her plans, but said after the meeting that she would make an announcement in two or three months.

She said she is worried about lethargy among blacks who have "made it. I don't see the kind of drive . . . the kind of motivation" that got blacks where they are today, she said.

She called on her audience to "get out of this kind of quiescence" and recognize that "in order to get change, we have to move."

Not only must blacks fight to maintain their own positions, she said, but they must fight on behalf of those who have not "made it," yet who have played a leading role in fighting for civil rights. "Blacks who were educated were the ones who were able to take advantage" of civil rights advances, she said. "We forgot . . . whence we came. . . . We forgot to look back to recognize that we too had a responsibility."

Are you prepared to take up the challenge "or are you so caught up in your own little life?" she asked the audience. "The fact that you are making it," she said, should not be an excuse for inaction.

"I am not here today to scare you," she added. "I am trying to prepare you for what is coming. Too often what we do is react, react, react because we don't prepare."

If present trends continue, she said, "we may very well have to resort to the techniques used in the 1960s. We don't have today a Malcolm X or a Martin Luther King. But we may have to use some of their techniques, particularly the nonviolent techniques of Dr. King . . . because we can't allow them to take us back to where we were. We can't allow them to do this."