Maryland's highest court ruled yesterday that divorced women who are able to do so must help support children of the marriage.

The unanimous opinion by the Maryland Court of Appeals applied for the first time the state's Equal Rights Amendment to the question of child support, according to Chief Judge Robert C. Murphy, who wrote the opinion.

The decision, which upheld in large part an earlier decision by the Maryland Court of Special Appeals, is part of a growing body of law across the country in which courts are holding women equally or partly responsible for financial care of their children.

"In applying the mandate of the (state) Equal Rights Amendment to the case before us, we hold that parental obligation for child support is not primarily an obligation of the father, but is one shared equally by both parents," Murphy wrote.

The decision threw out the old common law doctrine that the fathather is solely responsible for financial support of children of the marriage. Murphy wrote, "The common law rule is a vestige of the past; it cannot be reconciled with our commitment to equality of the sexes," he wrote.

"Parents must share the responsibility for parental support in accordance with their respective financial resources," the court concluded.

The court ruled on the divorce case of Robert C and Florence Rand, which was originally heard in 1971 in a Montgomery County Circuit Court. The original decision ordered Robert Rand to pay alimony to his former wife and child support of $250 a month for their daughter, Virginia.

In 1975, Florence Rand successfully moved to increase child support payments to $480 a month because their daughter was in college. Her former husband appealed that decision to the Court of Special Appeals which agreed that since his former wife earned $15,000 a year she should pay $225 toward the daughter's support, while his share should be $325, based on a formula involving his $27,000-a-year income.

Yesterday's decision upheld the principle of shared responsibility for child support, but threw out the formula used by the lower court. The case was ordered returned to Montgomery County Circuit Court for a final decision on the respective amounts.

Neither Robert C. Rand nor Florence Rand could be reached for comment.

Since 1970, about three dozen states, including Maryland, Virginia and the District of Columbia, have passed laws giving courts discretion in ordering shared financial responsibility for child support. The Maryland Equal Rights Amendment to the State Constitution on which yesterday's decision was based was passed in 1972.

However, few judges have put the rulings into effect, usually finding that the father is better able to make financial support payments, according to Doris Freed, chairman of the American Bar Association's divorce law and procedure committee.

In recent years several groups composed primarily of divorced fathers have sprung up to advocate shared responsibility for child support. These groups include Fathers United for Equal Rights and Men's Equality Now, which claim several thousand members coast-to-coast.