After a three-year deadlock, Lena Santos Ferguson, a black Washingtonian, has been admitted as a member at-large to the Daughters of the American Revolution.

"Alleluia," Ferguson said Friday. On Thursday she received a membership certificate, dated April 16 and signed by the national officers.

The national president, Mrs. Walter Hughey King, was unavailable for comment yesterday, but an assistant said three years was "not an unusual length of time." The assistant said she was not sure how many blacks belong to the DAR. "I know of four members, myself."

Said Ferguson: " . . .The main thing is, I wanted my ancestor recognized for serving during the American Revolution. Also, I wanted to be in a position to help other blacks who might be interested and who didn't know which way to turn."

Ferguson, an administrative secretary at Our Lady Queen of Peace School in Southeast, originally applied for membership in a local DAR chapter in 1980. She believed she met DAR standards. Her great-great-great-great-grandfather, John Gay, a white farmer who had served on the Meduncook (now Friendship), Maine, Committee of Correspondents, had been accepted as her nephew's entry to the Sons of the American Revolution and Ferguson had one sponsor from the chapter. However, the local DAR told her she needed two sponsors. Even after she met that requirement, the chapter didn't respond to her application. Then the DAR national office suggested she apply for the at-large category; initially she balked, thinking the local refused her solely because she was black.

"I had so many obstacles put in my way. I wasn't getting anywhere. So in March I decided to apply for the membership at-large, so at least I would have my papers authenticated."

Ferguson said she is joining the DAR mainly to use its research resources, take part in patriotic activities and so that her ancestor can be recognized. And she hasn't given up on local chapter membership.

"I'm thinking as I get older, I will have more time on my hands, and I probably would like to join a local chapter," said Ferguson, who is in her early fifties. "But right now I am putting that goal on the back burner."