The letter was written in cool antiseptic legal language, but to Barbara Bernhardt the meaning was clear: tomorrow, she must return to a Washington adoption agency the little girl she has called her daughter for 2 1/2 years.

Bernhardt has fought this demand in the Maryland courts since 1976, but one legal observer now says that "barring a miracle, the court case is over."

Still, Bernhardt cannot believe what is happening. "I don't know how anybody can come to the point of actually coming here and taking Deborah away," she said.

On Aug. 18 the Maryland Court of Appeals, the state's highest court, refused to hear Bernhardt's appeal from a lower court ruling in the case. This left standing a Montgomery County Circuit Court decision that a child welfare agency in Deborah's native Texas had the right to remove Deborah from the Bernhardt home in Takoma Park.

A letter from the lawyer for the Washington adoption agency that actually placed Deborah for the Texas agency, soon reached Bernhardt. It said an attempt would be made to have her held in contempt of court if Deborah was not returned to the agency - In Lutheran Social Services of the National Capital Area - by Wednesday.

Yesterday, as Bernhardt watched Deborah Annette, who is just shy of 3 years old, tug on a plush, purple elephant, she said she still did not know what she would do. "I hope that somebody, somewhere will listen and make them (the agencies) change their mind."

The Texas agency, according to testimony in the Circuit Court case, has wanted to remove Deborah partly because Bernhardt is now divorced and Deborah's natural mother wanted the child to have a home with both a mother and father.

Lutheran Social Services also has charged in court that Bernhardt concealed the fact that she and her husband were separated shortly after Deborah was placed in their home for a trial period in March 1976.

After learning in July 1976 of the separation, the agency reopened its investigation of the couple's "suitability" as adoptive parents and ultimately recommended that Deborah be removed from the home.

In December 1976 the Texas agency requested Deborah's removal, and the legal tug-of-war over the little girl began.

Bernhardt now says that she did not tell the agency of the separation because she and her husband were then trying to "patch things up" and she believed they would remain together. "It was a mistaken decision," Bernhardt says in looking back.

"But now it's 2 1/2 years later, Deborah is 3 years old . . . and the penalty for what I did should not be breaking up Deborah's life," Bernhardt says, her voice quavering.

"I also think all of this misses the point now. I am not an unfit mother by virtue of having not told the agency something nearly 3 years ago."

Bernhardt has two sons, 6-year-old David, and 5-year-old Daniel, who is also adopted.

And the courts have never in fact been asked to rule on Bernhardt's fitness as a mother.

Instead, the lawyer for the agencies has argued in Circuit Court that the agencies "made a mistake" in placing Deborah in the Bernhardt home and were simply trying to rectify this.

Although Deborah is a biracial Chicano-black child and Bernhardt is white, no one has raised race as an issue since the controversy over her adoption became public.

The Rev. Raymond Hartzell, director of Lutheran Social Services, refused yesterday to comment on the merits of the case or his agency's future plans for Deborah.

Asked if the agency would change its recommendation for removal at this point he said, "No."

Yesterday, on the front steps of Lutheran Social Services on 16th Street NW, two friends of Bernhardt handed Hartzell petitions with 650 signatures asking the agency to reconsider its decision and to leave Deborah in the Bernhardt home.

Jayetta Hecker, in tears, pleaded with Hartzell: "This is her family. Don't take her and give her to strangers."

Hartzell said he "respected" Hecker's opinion, but added: "The court has thoroughly dealt with this issue and made its decision. We must stick by that."