Carolyn Dock of Frederick, Md., is braced today for an emotional Christmas Eve telephone call.

If Army arrangements hold, she will talk to her son, 20, for the first time since he was sentenced to death for murdering a taxi driver in West Germany.

Pfc. Todd A. Dock will be calling from Fort Leavenworth, Kan. He will be executed there, perhaps by hanging, unless the sentence imposed after his court martial in November is revised or vacated.

Dock, according to court records, was drunk on June 12 when he allegedly robbed and repeatedly stabbed the cab driver who was driving him along the highway between Butzbach and Giessen. The soldier, 19 at the time, pleaded guilty.

His mother and her new civilian lawyer, confronted with the confession that has stood up through one trial, are trying to save the Dock from the gallows by putting the Army on trial.

The mother insists that the Army failed its responsibility to look after its own. She said her son was such an obvious, habitual drunkard while he was in the 3rd Armored Division at Ayers Kaserne, Kirchgoens, West Germany, that his superiors should have stepped in to save him from himself.

"They had him 24 hours a day," she said in an interview. "Why didn't they do something for him? He never knew what he was doing when he got drunk."

James R. Klimaski, Dock's civilian lawyer, said he will contend in the legal challenges that today's Army takes people in and throws them away when they become problems because there is a long line of people waiting to join the service.

"If you go into the Army as a boy, you have to go out of it as a boy," he said. "You can't be all you can be because there is no longer the small-unit leadership that turns a boy into a man."

Charles C. Moskos, Northwestern University sociology professor who has made intensive studies of the all-volunteer Army, agreed that "as the Army turns more occupational than institutional, the noncommissioned officers become more like shift bosses" than the 24-hour supervisors of earlier times.

"But," Moskos added, "bad apples were still bad apples then and now." He did not know the details of the Dock case but cautioned that there are some soldiers who behave unacceptably no matter what leadership they are given.

Army leaders are constrained from giving their side of the story until the Dock case makes its way through the standard review process. Unofficially, Army officers contend that small-unit leadership is better than ever in many units and that it is unfair to expect commanders to solve problems that families and civilian institutions could not solve.

Carolyn Dock said she will try to open the military's eye to the drinking problem in its ranks. "If I can't save my own son," she said, "maybe at least I can save someone else's."

This mother of six adopted children said she saw her son plunge into alcoholism after being an outstanding high school student, leader and athlete in Frederick. Neither she nor her son, she said, managed to overcome his drinking problem before he suddenly joined the Army in a fit of remorse.

Todd, she said, felt that his father, Joseph S. Dock, an aerospace engineer, did not like him as much as his brother, Adam, and became openly resentful. Joseph Dock died at work on Dec. 3, 1981, six days before Todd's 17th birthday.

"I didn't realize at the time that Todd figured he had caused his dad's sudden death," Carolyn Dock said. "The first time I realized he was into drinking was the summer of 1982, between his junior and senior year. I came home from a trip and the entire liquor cabinet was gone.

" 'Don't worry about it,' he told me, 'I won't do it again.' "

But he did. Many times. Danger signs were flying during his senior year of high school. He announced in December 1982 that he was joining the Army.

"He told me, 'I have to have some security.' His father had suddenly died on him the previous year, and he was afraid something would happen to me and then he wouldn't belong anywhere . . . ."

Carolyn Dock recalled that Todd said "he wanted his freedom" for the rest of the time he would be a civilian. He moved out early in 1983.

His promising future quickly exploded. "He drank and drank and drank," his mother said. He missed so many days of school in the last half of his senior year that he could not earn his high school diploma. This cost him the $8,000 bonus he would have received as a high school graduate joining the combat units of the Army. But he managed to get into the Army anyway, leaving Frederick for Fort Knox, Ky., in August 1983.

Once in the Army, Todd Dock drank heavily on occasion and was punished once for being abusive to a superior, his mother said. He received a nonjudicial punishment short of a court martial, while training to become a tank crewman at Fort Knox.

Carolyn Dock said Todd telephoned her after the incident and said, "I really got to have a problem because I don't remember what happened or what I did."

"He said he was going to get counseling when he got to Germany," she said. "That incident really scared me because he was having blackouts."

Her concern heightened to alarm, she said, when Todd came home for Christmas leave last year shortly before flying to Frankfurt, West Germany, to join the 3rd Armored Division. She said her son came into her bedroom drunk and went into a jumbled tirade. She said he snapped a lighter on and off under her face and pushed her back onto the bed when she tried to leave.

"It was the only time I was afraid of one of my kids. The next day I told him, 'You've got to leave.' He didn't remember a single thing that had happened. When I told him what he had done, he said: 'Mom, I'm so sorry. Can you ever forgive me? I love you so much. How could I have done anything like that?' "

Todd Dock left for Frankfurt last January. On July 6, his mother received an ominous phone call.

"I'm from CID," the caller said. "Your son has committed a crime."

She said the caller would not specify the crime over the telephone but made an appointment to come to the house. "I didn't even know what CID was," she said, in giving the initials for the Army's Criminal Investigation Division. "I couldn't sleep for three days." Then she was informed in person by CID officers that her son had been charged with murder.

"Utter disbelief. That was my reaction."

She pulled herself together, rounded up a thick batch of testimonials from teachers, principals and others about Todd's achievements and character. Some of the letters were entered into the trial record. A 10-member jury pronounced Pfc. Dock guilty of robbery and premeditated murder in what has been described as a grisly stabbing.

Army officals at the Pentagon said they could not give any details on the crime or discuss what alcoholic rehabilitation the service might have attempted on the teen-ager who turned violent when he drank. The Army's side of the story must await the release of the court transcript. The Army last hanged a soldier in 1961.

If Maj. Gen. Richard G. Graves, commander of the 3rd Armored Division, approves the trial record and the sentence, Todd Dock's conviction will go to the Army Court of Military Review. If no changes are made there, the case moves on to the Court of Military Appeals. After that, Todd Dock can appeal to the Supreme Court. The president must approve any military execution.

Carolyn Dock said she has not talked to her son since they waited in an anteroom off the Frankfurt courtroom to hear his sentence. She recalled that her son cried and said, "It's terrible to be hung for something you can't remember doing." The military jury heard that Dock left the Army base with a knife intending to robbing someone. That testimony helped build a case for premeditated murder.

Carolyn Dock said she had doubts about her son's guilt and felt that the extenuating circumstances of his drinking were not sufficiently considered during the trial.

"I feel the Army has culpability. We want a new trial," she added.

She said she does not know what she will say to her son when she talks to him today.