St. Mary's Seminary College in Cantonsville, Md., the undergraduate school of the nation's oldest Roman Catholic seminary, will close at the end of the school year because of declining enrollment.

The problem reflects a nationwide pattern of falling enrollments and closures at seminaries over the past decade. These institutions help prepare men for the priesthood while also providing the usual curriculums of high school and college.

Enrollments nationally have dropped from 45,767 in 1967 to 18,268 in 1976, according to recent statistics.

"We've seen the signs of the times," said the Rev. William Lee, president of the seminary and of St. Mary's Seminary College. "We're not weeping over the decision" because seminary colleges are becoming outmoded, he said.

St. Mary's peak year was 1969-70, when it had 320 undergraduates. This year's total is 106.

Father Lee cited several interrelated factors in the downward enrollment trend. He said students are making career choices at a later age and dioceses are opening less expensive religious formation houses near secular colleges for pretheology students instead of supporting full-scale seminary colleges. In some cases, bishops and future priests are selecting a more structured and conservative educational format that that offered by the progressive Sulpician Fathers, which operates St. Mary's.

"We are convinced students are going to make their vocational decisions at an older age, and the will have to have a lot clearer commitment to the ministry, probably by some practical training, before they got to seminary, Father Lee said.

Father Lee said it is difficult to assess why proportionately fewer men are becoming diocesan priests (who primarily hold parish jobs and are responsible to their bishops) than entering religious orders, in which men take vows of poverty, chastity and obedience and generally engage in specialized ministries.

"But we do knew that the diocesan priesthood is in considerable disarray. There are tremendous pressures in the parish. The whole concept of the priesthood has changed from the pastor who was absolute lord and master of his parish to one who has to deal with parish councils, permanent deacons, boards of education, and in some places angry women.

"It's a three-ring circus and the pastor is supposed to coordinate this. Many priests have no idea how to work in a team," Father Lee said.

Earlier retirement of priests also has affected seminaries, said Father Lee, who has headed the institutions since 1972.

"The seminary has become a very tough business. It used to be that older priests would 'retire' by teaching in th seminaries and slow down. We rang a bell when the students were to get up and when they were to go to bed and we told them every-thing to do in between. West Point was a snap compared to the old-style seminaries," he said.

Now the students can get up and go to bed when they want, have cars on campus, get field education off-campus, choose from a variety of courses and make most decisions about their personal life-style while in Sulpician colleges.

"We give them a considerable amount of freedom. The old style was much easier to administer, but I personally think what we're doing is a much more meaningful job of helping men undergo an internal conversion of faith," Father Lee said.

"In the past, the candidate was to conform to a fixed set of standards. Now we get the student to make personal response to a set of values. When he shows up in class, he comes because wants to. Before if he didn't he would be thrown out of school."

The Sulpicians operate four college seminaries in the United States. Another (in Seattle) also will close in June. The other institutions are in San Francisco and the Theological School of Catholic University in D.C.

Lee said the average of Sulpician seminary students now is 27, contrasted with 20 to 22 a few years ago. He said a challenge to seminary educators is to meet the needs of the older students.

The original St. Mary's Seminary opened in 1791 on what is now N. Paca Street in Baltimore. That property was closed in 1969 and sold to the city for a park in 1975. But the original church, built in 1808, the first gothic chapel in the United States, and mother Seton House next door remain as historical landmarks. The present theology school is located in Roland Park in north Baltimore.

The future of the 125-acre seminary college site in Cantonsville is yet to be decided, Father Lee said.

In the coming year, th Sulpicians, aided by a 23-member clergy-laity board headed by Archbishop William Borders of Baltimore, will consider how the order should be educating priests in the future. Three of the board members are women.

Until a year ago, the Sulpicians made their own decisions. However, said Father Lee, "The training for the priesthood is too complex and important to be left in the hands of the clergy. The people have to give us a much clearer concept of what they want, and they are taking much more initiative in this."