Within the past year, she has been cast out of the faith that has been her family's birthright for five generations.Her 20-year marriage ended in divorce. Her parents have all but disowned her, and she has been jailed.

But Sonia Johnson has not merely survived; she appears to be flourishing. "I think it has been perhaps the best year of my life," she said softly during a recent interview.

Then she paused before trying to explain that statement. "It's like Dickens says in 'Tale of Two Cities': 'It was the best of times; it was the worst of times.'"

Just a year ago, in an action that made national headlines, Johnson was excommunicated from the Church of Jesus Christ of Latter-day Saints because, church leaders said, she had defamed church leaders. But Johnson insists she was ousted because she fought vigorously against the church's opposition to the Equal Rights Amendment.

Six weeks after her excommunication, she and her husband separated and subsequently divorced for reasons that had nothing to do with her feminist convictions or her church troubles. Since then, she has been busy reordering her life and the lives of her four children, aged 6 to 17.

"A year ago, I thought, 'oh, if I can just get through the year,'" she said, "but you know, this year has been wonderful!" Seated on a dark-blue couch in her sun-washed living room in rural Loudoun County near Sterling, Johnson looks like a woman at peace with herself. The strained and tense look of a year ago is gone; her eyes sparkle and her smile comes easily and often.

With unmistakable triumph, she said, "I found out that on my own I can support these kids and do it in the style to which they had become accustomed." sShe is providing for her family by working for the cause closest to her heart: slecturing on equal rights for women.

The children, she said, "are very proud of me. I think the period of mourning about the divorce, the period of mourning over my misery [over being ousted from the Mormon church] . . . is largely over."

". . . I have far fewer fears. Oh, of course, there are things I am afraid of, but I know that no matter what comes, I am equal to it. What was it that Camus said?" -- and she struggles to recall the precise words of the French philosopher-writer -- "'In the midst of winter, we know we have in ourselves as invincible summer.'"

The real secret of her survival, Johnson said, is "the women out there in the women's movement. They are so supportive. I go out there and tell that story," of her explusion from the Morman Church "and it's like having 1,000 psychiatrists. I've told the story over and over again till I've exorcised the pain . . . I just have never felt alone."

Since her troubles with her church hit the press a year ago, she has gotten more than 5,000 letters, "every one of them saying: 'If you ever need anything. . . .' My word, if I weren't happy, I would be an ungrateful wretch."

Well, not quite every letter she received was supportive, she acknowledges: perhaps 15 percent were critical, with "98 percent of these coming from Mormans."

Her relationship with her parents in Utah, traditionally so important to Mormans, who believe that families are together throughout all eternity, is "very strained." "They are just shocked and dismayed all the time by what I am doing. . . .They call me and tell me all the time that I am in spiritual danger." The relationship may be close to the breaking point. "I can't carry them around on my back. . . . I can't afford the weight of all their worries about my eternal life.

"I'm sad about that [the rift with her parents]. I hope if I don't do anything outrageous for a month of two, they'll regain their equilibrium. But I have told them that this is just the begining. . . . I really do mean it when I say I am willing to give my life for this cause [of full equality for women] if that is what it takes."

The most recent assault on her parents' sensibilities came early last month when Johnson and 20 others were arrested when they chained themselves to the gates of a new Morman temple in suburban Seattle, as part of her continuing protest of the church's opposition to ERA.

But if Johnson's parents were traumized by newspaper photographs of their daughter marching off to jail still draped in her chains, her children had a different reaction. "I was supposed to come back home that night," she said, "so I had to call them and tell them that I was in jail," she said. "Kari [her 15-year-old daughter] said, 'Oh, congratulations!' and Mark [who is 12] came on the phone and said, 'Mom, I'm so proud of you!'"

The three children who are with her -- a son, Eric, 17, is finishing high school in Utah because Loundoun County is asthma country for him -- took some flak from schoolmates a year ago when their mother's church trial was in all the papers. But all three, she says, are committed feminists.

"Even my 6-year-old came home from school one day and said all the children that day had to talk about their families," she recalled. "I asked him, 'What did you say?' and he said, 'I told them I come from an ERA family.' They know what we're about in this family."

She said she is not bitter about the divorce. "I don't feel animosity. I don't feel hostility," she said. "I just feel comfortable."

Johnson said she has thought about remarriage "because people ask me that, but I'm just enjoying being single now. I suspect that as time goes on, there will come a time when I will be lonely for male companionship . . . I liked being married," she said.

With all her strong feminist views, she is not anti-men, Johnson said. "Personally, on a one-to-one basis, I like [men] a lot. How can I not like them? I've got three sons. What society has done [in male-female relationships] is vile for them."

She points out that a third of the members of Mormans for ERA -- whose membership has increased from 500 to 1,200 im the wake of her battles with the church -- are men. She is president of the organization even though, technically, she is no longer a Morman.

Until October, Johnson still went every Sunday she was home to the Morman congregation in Sterling whose bishop brought the excommunication charges against her. "I wanted them to know that I hadn't disowned them; they disowned me; to remind them of the problem I represented.

"I knew I was the symbol of that problem [of the male-dominated attitude toward women], and I wanted to be there to remind them of that. But it got to be so painful . . . like going to a funeral every Sunday; like somebody you loved with all your heart and soul now is dead and will never be alive again."

So she has stopped going to church, convinced that while some churches have made some progress toward reducing male domination, it continues to be a problem in every denomination. "As far as I know, most churches in this country, maybe in the world, are male-owned, male institutions," she said. "I don't really have much interest in religious institutions that make only half the people feel whole. I am only interested in a religion that empowers everybody, that makes everybody feel worthy.

"I think that the church that does that will have to have female representation among the gods" -- the beginning of a smile twinkles in her eyes -- "We'll have to have an Equal Rights Amendment in heaven."

Johnson is not about to give up on ratification of the Equal Rights Amendment just because an administration hostile to it is coming to power, and anti-ERA forces gained ground in all of the unratified states. "We will not give up until 12 o'clock midnight, June 30, 1982," when the ratification time of ERA expires.

The Reagan White House, she suggested, may be the next target of a campaign of nonviolent civil disobedience. "It was hard to protest against the Carter administration," she said. "We knew they weren't doing anything, but the rhetoric was so good! But the situation is no longer ambiguous. It is quite clear that the enemies of women are in the White House."