Ronald Elza, a stocky ex-marine, took the witness stand today in Anne Arundel County Circuit Court and tried to convince a judge who had already once refused him that he could raise his 6-year-old daughter better than her mother.

"If I had the child, it would be me taking care of Shannon. I would cook and clean," Elza said, groping for words to convince Judge Robert S. Heise that he could do such tasks. "I will be taking care of the child full time."

It is a drama played out often in courtrooms around the country. Divorcing parents want custody of their children and try to prove who is better equipped to take them. In the vast majority of cases, says Elza, the mothers win, even in states like Maryland where the law mandates equal treatment of parents in custody battles.

So Elza, a 34-year-old disabled Vietnam veteran, says he isn't just fighting for himself, but for fathers everywhere who are denied custody solely on the basis of their sex.

He lost his first attempt to get Shannon in June 1983 when Heise, according to court transcripts, awarded custody to the mother stating, "I suppose I am old-fashioned in one sense . . . but it still seems to me, that if it's a 5-year-old . . . and with all other factors being equal . . . the child should go with the mother."

Maryland's highest court nullified Heise's decision, stating its support for the 1974 amendment to Maryland law that mandates "equal treatment of parents." The court asked Heise to hear the case again.

Today, Heise said that in order to help him make his decision, he will call Shannon Elza herself, a bright-eyed pixie of a girl with platinum blond hair, to take the stand and tell him whether she wants to live with her mother or with her father. Heise said he will talk to the girl in open court, possibly in the presence of her parents.

Although Elza won the appeals court battle, the odds still are not in his favor, said Bruce Burrows, president of the Montgomery-Prince George's counties' chapter of the Fathers United for Equal Rights Foundation. According to a survey done by his group and a national survey done last year, as many as 90 percent of all contested child custody cases are awarded to mothers, he said.

"No longer can judges verbalize the maternal preference doctrine," said Burrows, a divorced father with custody. But, he added, women are still favored. "If Heise hadn't said that, it would have been unassailable.

"There is still an attitude that if you wear a skirt you're better equipped" to raise children.

Susan Elza, who is now living in Pasadena, a community 10 miles north of here, did not outline today why she believes she should have Shannon, other than the fact that she has spent most of the last six years raising her and only took a full-time job as an administrative assistant this year.

She took Shannon and left the family's home in Westmoreland County, Va., in May 1983 because she was afraid of her husband, she said, explaining that the marriage had deteriorated into arguments and threats that upset the little girl. She said her husband, although retired on a full military disability pension, was so involved in community affairs that he gave his family little time.

"Shannon and I were more or less on our own," she said.

Their divorce, which is pending in a Virginia court, is expected to be final by the end of this month.

When it came time for Ronald Elza to testify today, he said that he should have Shannon because he could be with her all the time. Suffering from wounds caused by shrapnel and a mortar shell, he doesn't have a job, but his disability pays him $2,200 a month.

Yet to testify in the custody hearing is a psychologist, Marianne Cordahl, who has seen both Shannon and her mother for more than a year. Shannon's testimony would follow Cordahl's, but no date has been set for either's testimony.