John M. Fedders, who resigned a top post at the Securities and Exchange Commission amid widely publicized charges that he beat his wife Charlotte, won the first round yesterday of a bitter legal battle for a financial share of her new book, "Shattered Dreams," the story of their tortured marriage and the domestic violence that caused its collapse.

In a decree that drew an immediate angry reaction from women's rights groups, a Montgomery County divorce court official held Charlotte Fedders and her husband equally responsible for the breakup of the marriage and awarded John Fedders 25 percent of her book proceeds.

Fedders, who resigned as SEC enforcement chief in 1985, had testified that his former wife should share blame for his violent outbursts because she denied him emotional support during his bouts of depression.

Domestic Relations Master John S. McInerney, in his 12-page decision, agreed with Fedders:

"Overall, the circumstances that contributed to the estrangement of the parties has got to be on an equal basis," he wrote. "There is no question that the plaintiff suffered physical abuse, but that, in and of itself, was not what brought about the estrangement of the parties."

Charlotte Fedders' attorney, Bryan Renehan, said his client will appeal the decision, which also granted John Fedders a half interest in the couple's $425,000 Potomac house and reduced Fedders' monthly alimony payments by one-third.

The order by McInerney, a former three-term Republican state legislator who has been a divorce arbiter for 11 years, will take effect unless Charlotte Fedders wins an appeal to the Circuit Court. In Maryland courts, domestic relations masters preside over divorce cases and rule on the division of assets.

"It's just so outrageous there are no words for it," said Molly Yard, president of the National Organization for Women. "She was the victim of her husband and now she's a victim of the court . . . I think it sends a terrible message to wife beaters."

"Absolutely appalling," said Marcia Niemann, director of the National Coalition Against Domestic Violence. "There is just no good reason I can think of to justify a court decision like that."

Fedders, who testified last month that publicity generated by the divorce had ruined his successful legal career and left him strapped for money, issued a brief statement through his attorney yesterday, but declined further comment on what he called "our private family matter."

"The court opinion speaks for itself," he said in the statement.

Charlotte Fedders, in St. Louis on the first leg of a 17-city tour to promote her book, called the ruling "an atrocity."

"I am fairly outraged," she said. "I expected a lot of things, but not the book. This, in effect, means I am supporting my husband. It puts the battered women's movement back years."

Her attorney said the ruling shows "a lack of understanding of the dynamics of domestic violence."

In emotional testimony before McInerney on Sept. 16, John Fedders cited his mother's prolonged absences during his childhood as the cause for his spells of depression as an adult. He said his wife provoked him to violence by denying him emotional support, occasionally even baiting him with bitter suggestions that he commit suicide.

Fedders, a presidential appointee who was paid $72,300 a year at the SEC before his wife's charges gained national attention in 1985, testified that his image and legal career were ruined. He was paid $160,000 a year at the prestigious Washington law firm of Arnold & Porter before moving to the SEC in 1981. But he testified that potential legal clients were shunning him and said he expected to earn only about $30,000 in private practice this year.

In describing how his marital troubles affected him, Fedders, a 6-foot-10 former Marquette University basketball player, testified that he was seeing a psychiatrist early each morning, then attending Roman Catholic mass before starting work at his small office on Wisconsin Avenue NW.

In her testimony a day earlier, Charlotte Fedders portrayed herself as a busy mother, struggling on a limited income to make ends meet and provide a full life for their five sons, ages 6 to 18.

She testified that her estranged husband, whom she married in 1966, paid her $750 a month in alimony and $750 in child support. She said she supplemented that with about $300 a month from a part-time job in a flower shop. She asked McInerney to award her the Fedderses' house in Potomac, where the couple lived before she filed for divorce on June 22, 1983.

Renehan said his client had intended to sell the house, buy a smaller one and use some of the leftover money to pay old bills.

John Fedders, besides requesting lower alimony payments, asked McInerney to order the house sold and award him half the proceeds.

McInerney met both requests. Citing Fedders' sharply reduced income, he cut the alimony payments to $500. He also ordered Fedders to pay $3,000 of his estranged wife's outstanding legal bills, although she had requested full payment of the estimated $20,000 debt.

Charlotte Fedders' book, written with Washingtonian magazine staff member Laura Elliott, began appearing in stores last week after the publisher, Harper & Row, ordered an initial printing of 50,000 copies. An official of the Association of American Publishers said that the number of copies printed indicates high sales expections by Harper & Row.

In her testimony last month, Charlotte Fedders said she had received $47,700 of a $100,000 publisher's advance that she shared with Elliott and their agent. She said she could not estimate how much she will earn in royalties, nor when she will begin receiving them.

She testified that Dell publishing paid Harper & Row $300,000 for paperback rights, but did not say whether she will receive a percentage.