The trustees of Trinity College, a Catholic women's school in Northeast Washington, have chosen James J. McGrath as the college's new president, the first man and first person not a member of a religious order to hold that post since the college was established 90 years ago.

McGrath, 57, is president of William Rainey Harper College, a public two-year community college in Palatine, Ill., in the northwestern suburbs of Chicago.

"We decided to pick the best candidate, what Trinity needs at this time," said Sister Regina Finnegan, head of the college board of trustees, which has 17 women and nine men. "But we are committed to remaining a Catholic women's college."

After the resignation of Sister Donna Jurick as Trinity's president last spring, the trustees rescinded the requirement that the president be a member of the Sisters of Notre Dame de Namur, the religious order that founded the institution.

"We felt we wanted a wider pool of prospective candidates," Finnegan said. Membership in the order has declined substantially in the last two decades, as it has among other groups of Catholic nuns.

Trinity's enrollment also has dropped since the mid-1960s, a problem that occurred in many women's colleges after most all-male schools became coeducational.

In recent years, enrollment stabilized with the addition of a weekend college, offering evening courses to older women. But that change, which Jurick spearheaded during her five years in office, stirred severe dissension. When she resigned, Jurick said a "consensus" had not been reached among faculty, students and alumnae to support "the direction I have taken."

Last year, the college had 961 students, including 344 full-time regular undergraduates; 378 students in the weekend college; 82 part-time undergraduates, and 157 graduate students, most in education programs. All students were women except for 21 men in graduate courses.

Some student leaders said last year they were fearful that Trinity was not focusing sufficiently on undergraduates of traditional college age. Several faculty leaders said there had been a loss of "collegiality."

In an open letter, Finnegan and Cathleen Black, the publisher of USA Today who headed the search committee, said the decision to select a lay person and man as Trinity's president "was a source of deep introspection and intense discussion."

But "on balance," they said McGrath was chosen "given Trinity's great need for stability and sound fiscal management, restoration of collegiality, and confident leadership."

In an interview yesterday McGrath said his "major commitment at Trinity College will be to the full-time students," and added, "I feel very strongly about the traditions on campus."

Marcia Sharp, executive director of the Women's College Coalition, said about a quarter of the presidents at the nation's 100 women's colleges are men, a proportion that is down substantially over the past two decades. She said the appointment of a man to head Trinity "may send a message of men and women working together for women's education."

Since 1970, about two-thirds of women's colleges in the country have turned coed, including Goucher and Marymount this year.

Before going to Harper College in 1978, McGrath held administrative posts for 20 years at the City University of New York, including university dean for academic affairs under the Rev. Timothy J. Healy, now president of Georgetown University.

Healy said in a statement that McGrath "is quite simply the ablest and most pleasant university administrator with whom I have ever worked."