When Chief Justice Harold H. Greene of D. C. Superior Court announced yesterday he would not order Jeremiah Winstead, a member of the Church of the New Family, into the custody of his mother, the courtroom erupted into loud cheers and Winstead's lawyers hugged each other.

The excitement and disappointment, however, had nothing to do with "Winstead," his "church" or his "mother." What Greene's decision meant was the "lawyers" from Ballou had defeated their opponents from Coolidge for the championship of the D. C. Street Law Project's high school mock trial competition.

Street Law courses, which are geared to educating people about the law and its role in their everyday lives, are taught in 26 public high schools around the city by area law students who earn academic credit for their efforts. The Street Law Project, funded by the public school system, is sponsored by the Georgetown University Law Center, where yesterday's mock trial was held.

The two-hour all-student trial involved all the elements of standard courtroom procedure - and more. The bailiff was appropriately stern, the witnesses cried or acted belligerent on cue, exhibits were introduced into evidence and the lawyers were polished and prepared for their day in court.

In the end, the competition between the petitioners and the respondents over a D.C. law that allows the courts to appoint custodians was fierce enough to suit a championship basketball game.

When Greene announced Coolidge had lost only the case but also the championship, one Coolidge lawyer dropped his head to the table where he sat. Later, another broke down in tears.

"It's to the judge and the judge ruled against us," said Coolidge lawyer sherry Dawson, who along with Lorenzo Washington, Pamela Richardson and Keith Hoppes represented Martha Winstead - Jeremiah's mother.

Meanwhile, Ballou's legal team of Jacqueline Kinlow, George Smith and Larry Williams, all of whom represented Jeremiah along with their street law teacher, Georgetown law student Edward Hochman, busily accepted congratulations and the championship plaque from Vicent Reed, D. C. school superitendent.

"We know there are no losers today," Reed said to the students, teachers and parents who filled the Georgetown moot courtroom to overflowing

Hochman explained the high school teams had worked with the same case through three rounds of competition until they made it to the final.

When it comes down to the championship, Hockman said, the contest turns oh the skills of the students lawyers, who by the time have have mastered the facts of the case.

Through the competition, Hochman and the other Law student in structors help the high school students master the rules of courtroom practice and assist in preparation of witnesses. During the trials, however, the students are on their own.

Hochman, whose forehead glistened with presiraption when the trial was over, said the hours the students spent in preparation "climbed well into the triple figures." But, Hochman said, "it's fun."

A prep school graduate, Hochman said the street law course was also a chance for him to "see an inner city school" like Ballou.

Street law "is like real life . . . it's exciting," said Mark Webb, 18, a McKinley High student who was the bailiff at last year's championship trial.

"You don't cut this class," Webb said, "you learn something."