Why would a feminist journal with an uncompromising ethos of self-achievement devote an issue to the secrets of marital longevity? And what's an exploration of the same theme -- more familiar to the traditional, family-oriented pages of a Good Housekeeping, Family Circle, Redbook or the like -- doing in the monthly bible of pop psychology?

Simple. Marriage -- particularly long-term marriage, it seems -- is in vogue again, displacing divorce as a subject of popular intrigue and speculation.

"There's a new ethic of commitment on the American scene," proclaims Robert Lauer, coauthor with his wife, Jeanette, of a study highlighted in the June issue of Psychology Today.

The assumption is shared by Francine Klagsbrun, whose probing new book, Married People: Staying Together in the Age of Divorce (Bantam Books, $16.95), is excerpted in June's Ms. magazine. Says Klagsbrun, a writer and lecturer on social issues, "I'm hearing it more: 'I want it to last.' I lecture around the country . . . and so many young people are asking because they're scared, with all the divorce around them . . . Isn't it interesting that Ms. -- of all magazines -- would have a whole issue on this. That's another indication that it's sort of in the air. Would Ms. five or 10 years ago have run something like this?"

Even among those rarities -- folks without books to sell -- there's some talk of a new, less casual attitude toward divorce. The claim, says William Baxter, a therapist at the Marriage and Family Institute in the District, "matches what I've seen and what I feel. People are really ready to work hard on their marriages." A counselor for 35 years, he says, "I hear people wanting to trust their own history, keep the rituals they've developed, worrying about their children and the price the children pay in a divorce.

A Washington psychoanalyst who asked not to be identified says he's struck by the degree of fidelity among his friends and fellow professionals.

What's unclear is whether the proclamations are an accurate reflection of a change in public sentiment or an optimistic attempt to shape it.

Statistically, there's little to go on. If only because of population redistribution, more people are marrying (a record 2.5 million couples tied the knot last year), but nothing suggests they're doing it better or longer. While 58 percent of first marriages now last more than 15 years, according to the National Center for Health Statistics, no figures are available to show if that percent is on the rise.

And while the national divorce rate dropped 8 percent (not 4, as Klagsbrun mistakenly writes) between 1981 and 1984, statisticians like to put that in perspective by comparing it to the 141 percent increase it's seen over the preceding 19 years. "We're not seeing a trend towards more stable marriages," says Deborah Freedman, research associate at the Population Studies Center of the University of Michigan.

Says Larry Bumpass, who studies marriage and divorce patterns as sociology professor at the University of Wisconsin, "We're still in a society where half of all marriages end in divorce. This is far more important a fact than whatever slight change may have occurred in the rate at which divorce has been increasing."

It's a little like the half-empty/half-full debate. Klagsbrun and company don't dispute Bumpass' figures. They simply prefer to concentrate on the half that succeeds rather than the half that fails. Independently, Klagsbrun and the Lauers decided to seek answers from long-married couples themselves, rather than offer formulas or distillations from so-called "experts."

Both Klagsbrun and the Lauers studied couples married 15 years or longer, reasoning that marriages of this duration have a better than even chance of continuing. (Half of all couples who divorce still do so at the treacherous seven-year mark, just as they did 10 years ago.)

But their approaches -- and findings -- are quite different.

Klagsbrun, married 30 years, interviewed at length more than 200 marriage partners, separately and together, whom she met or was referred to on lecture tours. She saw many of them several times and invited them to tell their own stories. Most, but not all, were first marriages. All subjects were promised anonymity. She blends their stories with her own highly personal impressions and experiences in a sophisticated and non-preachy narrative.

The method allows for complex findings and for the unexpected.

"One of the things I found that surprised me," says the author, "is that sharing interests is not necessary to having a good marriage. I know a lot of people don't agree with this . . . But what I think is very important if you're not sharing interests is sharing values: if the partners are both people who like giving charity rather than spending it all on themselves, if they both consider the kids terribly important in the marriage. I think underlying values have to be shared, whereas interests don't have to be shared. What we're always hearing is you have to have joint interests, but I don't believe that."

The Lauers -- Jeanette is a social history professor and Robert, the dean of the School of Human Behavior at the United States International University in San Diego -- surveyed 351 couples, starting with acquaintances, using a standardized questionnaire. Respondents were asked to describe separately such items as their areas of satisfaction and dissatisfaction, their methods of handling conflict and the ways they had changed.

In analyzing responses, the Lauers -- also married 30 years -- assume husbands and wives followed instructions and did not compare notes. This was admittedly hard to guarantee for the third of their respondents who lived outside California and were surveyed by mail.

What drama there is to the findings reported in Psychology Today hinges largely on the validity of this assumption. Here, couples were given a list of 39 statements and asked to choose which best explained why their marriage had endured. The winners, from the top: "My spouse is my best friend . . . I like my spouse as a person . . . Marriage is a long-term commitment . . ."

Says Robert Lauer, "One of the most revealing things we found is that although husbands and wives responded separately, the seven most frequently named reasons were the same." The probability of that happening randomly, he says, is very small.

The answers, he says, are instructive in other ways. "One thing they do is underscore the extent to which we still have a lot of myths about marriage in this country. A lot of people go into it thinking love is the answer. We had one woman answer, 'Love is what you go through with somebody,' meaning you don't know what love is until you've been with somebody for some time. I think it gets back to: How much are you willing to commit yourself to someone, to face difficulties together? These are things young people should be thinking about, not just how you feel about somebody else."

The Lauers also emphasize -- more than Klagsbrun -- the importance of shared interests, citing this as a source of strength in their own marriage. Says Jeanette Lauer: Respondents "certainly stress this many times, that they have interests in common, which is not to say they don't have separate interests as well . . . It stems out of the fact that they enjoy spending so much time together."

Some highly condensed points from among Klagsbrun's findings:

Most successful, long-term marriages endure periodic slumps and rises. Even the most "creative" marriage can't provide continual satisfaction and excitement. But duration is not always a measure of success: Some bitter marriages drag on out of need, pressure or inertia.

Partners in strong marriages have the "kind of paradoxical combination," says Klagsbrun, "of being able to change on one hand . . . and being able to live with things that can't change, things that are not perfect. I think one of the keys to staying married is not always thinking everything can be improved, and that if it can't be improved, it's terrible. You have to be able to say , 'These are some ways this person is not going to change, but there are enough other things here of value that I'm going to stay with it.' "

In most enduring marriages Klagsbrun studied, there was an assumption of permanence. "One woman said to me, 'There are times when we have the worst fights, and I have tears running down my face, and I scream, 'We're stuck together. We have to find something to do because we're stuck together,' and so we do.' "

What's the likelihood of a noticeable rise in long-term marriage?

Bumpass is skeptical: "Even if there is an increasing realization of how high the risks are, this doesn't imply an increased interest would have any effect at all on marital stability."

But family therapist Baxter, while equally cynical, notes there's no overstating people's hunger to follow a trend. "People are going to look at recent statistics and say, 'Oh, that's the style this year. We should not look at divorce. We should look at more marriage.' The statistics probably help predict the mood. We all want to be hip to the beat of the times."