The typical convert to Roman Catholicism today is likely to be a relatively well-educated woman under 30, who embraced the faith because she is, has been or is about to be married to a Catholic, according to a new study.

The reason most often given for dropping out of the church, according to Dean Hoge, a sociologist at Catholic University who directed the study, is that an individual has lost his or her "motivation" for attending mass. Disagreement with Catholic moral teachings runs a close second.

Though his own findings did not address the question directly, Hoge cited recent studies that estimate that "up to 80 percent of all [Catholic] church dropouts return to some church at some time in their lives."

Hoge's progress report on a nationwide survey on the motivations for joining, dropping out or rejoining the Catholic Church was made yesterday to the National Catholic Lay Celebration of Evangelism in session here.

For the study, Roge and his associates surveyed 200 persons in cash of three categories: convents, dropouts and returnees. The sampling came from parishes in seven dioceses: Baltimore; Detroit; Providence, R.I.; Orlando, Fla.; Omaha; Oakland and San Antiono.

In all categories, family consederation -- spouse, children or parents -- were the main reasons respondents joined or left the church.

Among recent converts, 38 percent cited marriage to a Catholic spouse as the primary reason for converting because their children were being reared as Catholics and they were concerned about their religious upbringing or the family's religious unity, Hoge said.

While he estimated that "about half" of those converting for the sake of family unity also reflected spiritual motivations of their own, Hoge said only 12 percent of the converts come into the church as "seekers," entirely on their own.

Such seekers, he said, "slightly older" than those converting for family reasons.

Hoge stressed that is usually took some event "such as a personal crisis, a religious experience or some component of a midlife crisis" to push the individual into the "inquiry class," which can lead to formal conversion.

Hoge also found that conversion rarely took place, whatever the motivation, without some sort of personal go-between or "friends or relatives with whom the convert has a trust relationship."

Hoge said that while intermarriage is increasing "the percentage of Non-Catholics who marry Catholics and then convert is decreasing." He said that "forty-percent of Catholics today marry non-Catholics," but about half these marriages "remain mixed marriages."

Of the other half, he said that in recent years, there may have been as many conversions of the Catholic partner to the spouse's faith as vice versa. This is in contrast to the situation 20 years ago, when three non-Catholics came into the church for every Catholic who left as a result of mixed marriages, Hoge said.

The highest rate of conversions is in the South Central section of the United States; the lowest in New England, according to Hoge. The reason, he suggested, is that more intermarriage takes place in "regions where Catholics are a small majority and where no ethnic or class barriers impede mixing."

Hoge said that his study of Catholic dropouts was "less reliable" than that of converts, since inactive Catholics "felt [in conflict] with the church and didn't want to talk about it" to researchers.

An inactive Catholic was defined as one who had attended mass fewer than two times in the past year, not counting weddings, funerals, Christmas or Easter.

He estimated that of the sample studied, "about 35 percent of those dropping out did so by 20 years of age and 54 percent did so by [age] 25."

For the yonger dropouts -- those 22 years of age and under -- more than half said they have left because their Catholic parents put too much stress on churchgoing, Hoge reported, adding that teen-age dropouts are "a problem in all Christian churches."

Nearly one-fourth of all dropouts studied cited their differences with the church's moral teaching particularly on "sexuality and marriage" as the reason for leaving. Hoge said.

Hoge said, "Some have life styles involving premarital sex, cohabitation, contraception, and feel too guilty to go to mass," he said.He added that "birth control and divorce are the primary problem areas."

An even larger number -- nearly one-third -- of the inactive Catholics cited a range of reasons that Hoge boiled down to feeling that they had "lost any motivation to attend" mass. "We heard many criticisms of the church from weary dropouts -- that the church is cold is impersonal that it is boring, that the priests are always talking about money, and that the church isn't Biblical or isn't necessary for the Christian life," he said.

Only 7 percent cited the changes in the liturgy and substitution of English for the traditional Latin as the reason for leaving. Hoge said a 1978 Gallup poll showed that more people drop out because of too few changes than because of too many.

"A clear majority of all the people we interviewed like the changes in the Catholic Church since Vatican II," Hoge said.

The sociologist's report was part of a five-day national conference on evangelization. That is designated to stimulate lay members to bring more nonmembers and alienated Catholics into the fold. The conference concludes tomorrow night.