When Lena Santos Ferguson wasn't yet a teen-ager, the Daughters of the American Revolution refused to let the great singer Marian Anderson perform in their Washington hall. Somehow, Ferguson made the connection between the public outcry over that act of bigotry and a portrait of her great-grandfather in a Civil War uniform over the mantel. "I thought he probably had ancestors who had fought in various wars. And I told my mother, 'I bet we could trace our ancestry and become members of the DAR,' " remembered Ferguson.

For the last two years, Ferguson has been trying unsuccessfully to realize that teen-age fancy. A nephew traced the family history and found that Ferguson's great-great-great-great-grandfather, Jonah Gay, a white farmer on her mother's side, had served the American Revolution effort as a member of the Meduncook (now Friendship) Maine Committee of Correspondents.

Ferguson, a black woman in her fifties who brings a good-natured sense of fair play to this small battle, belongs to the breed of gentle protester who watches from the sidelines until one incident causes long pent-up outrage to burst. That is the posture of the slim, long-haired woman sitting on the gold sofa of her Fort Dupont home, the scrapbooks of her black and white ancestors and her DAR-related correspondence and notes on her lap. Last month the third of her letters from the DAR, one suggesting she join as a member-at-large, made her angry.

"My conclusion was that they were offering me membership-at-large because the local chapter didn't want me solely because I'm black," said Ferguson, a school administrative secretary. "And this way the national is condoning the action of the local." Ferguson had also heard that both Marian Anderson and Leontyne Price were invited to participate in the DAR convention which opens here today and she was concerned that that gesture would be interpreted as a reform.

Two local DAR officials who are familiar with Ferguson's desire to join cited her sponsor's failure to follow DAR procedure as the reason Ferguson has come up short in her efforts. To be nominated, a prospective member must have proof of an ancestor's participation in the American Revolution and have two sponsors. Ferguson has only one. "Her sponsor is a person who has not done anything," said Eleanor Niebell, the regent of the Washington area. "I'm sorry Mrs. Ferguson is feeling this way." The DAR officials said the membership-at-large invitation was a sign the organization was trying to be helpful. But Ferguson's sponsor, Margaret Johnston, said all the chapter members she asked to co-sponsor Ferguson turned her down and that each time she brought up the Ferguson request, she was quoted the DAR bylaws. Johnston didn't want to discuss the issue of racism, saying, "Officially no officer has said to me, 'They don't want her because she is black.' "

Even though the DAR still has for many people a reputation as a conservative, bigoted group, Ferguson didn't anticipate any trouble when she decided to try to join. Five years ago Karen Farmer of Detroit, who was thought to be the first black member, joined apparently without being confronted with any major problems, and DAR officials repeatedly say the group doesn't keep records on the race of its members. In addition, Ferguson's ancestor Jonah Gay had already been used, Ferguson explained, by two white women on their applications. Maurice Barboza, a nephew of Ferguson's in Washington, used Gay and, ironically, the DAR library for some of his research to prove his eligibility for the Sons of the American Revolution. He was accepted in 1980, he recalled, without any delay or incident.

But Ferguson describes her encounters with DAR members as frosty. At a tea she attended, Ferguson was introduced by her sponsor as a prospective member. "Well," she laughed knowingly, "I had been in other situations like that when I first came to D.C. They were polite but nobody went overboard to make me feel welcome. Some said hello, then it was over and out."

In February, at an American Revolution descendants' dinner, Ferguson sat next to someone from the chapter she is seeking to join. "She gave me this advice: 'Don't push, things will work out, be patient.' Then she asked me why I wanted to join," said Ferguson, her face twisted with the unpleasant memory. "She said she wouldn't join an all-black organization. She said she didn't think she would be comfortable. I told her she would be made to feel welcome among my black friends. Then I asked her to sponsor me and she said she wouldn't sign for someone she didn't know. She was getting very upset. So I dropped it."

Even though she is angry, Ferguson still wants DAR membership to give public recognition to her family ancestry. Her posture is diplomatic, as well as gentle. For example, she declines to be photographed in connection with her protest because she wants the focus on her perception of the problem, not herself. "I am quite sure they do good works, scholarships and other things. I don't think most of the women in the DAR know this is going on. I must have hit on an isolated incident. I hope so," said Ferguson.

The episode stirs her memory of the first night she came to Washington from Connecticut in 1952. Arriving at the downtown YWCA, they told her they were unable to fill the reservation her new boss at the Navy Department had made. " 'What race did you say you were?' the woman on the desk asked me," recalled Ferguson. "Then she got her boss, who said they would clean out a room. All I could do was imagine them cleaning out a closet and putting a cot in it, so I wouldn't soil those little white girls." Her nephew, who was sitting next to her, said, "That's just what the DAR is doing by suggesting a membership-at-large." Ferguson nodded in agreement.