The Trinitarian Fathers, who created a furor a few years ago with their hard-sell appeal for priestly candidates in the pages of Playboy Magazine, have since quadrupled their crop of candidates.

While many other orders have been shrinking in size, the Maryland-based Catholic order has grown from 15 can-Catholic order has grown from 15 candidates for priesthood to 60 in the past five years, in large measure because of their ads in Playboy, Rolling Stone, Time and Newsweek coupled with their retention of age-old strict spiritual practices.

Men who enter the order still don the white hooded cassock adorned with a red and blue cross symbolizing freedom and live a monastic life at Trinitarian headquarters here in the country to the Northwest of Baltimore.

It was the Playboy ad in 1972 that sent the small obscure order of Trinitarians into national view. Two young men were pictured in casual clothes. The message began: "You are already a Trinitarian. You who have love to give and the courage to offer it, you are already a Trinitarian. Come work with your brothers. Come home.

"We tug at the sleeve of the Church and take it into the darkest corners of our society to bring help to people who are left out," it said. "In this time of anxiety and anguish, the Trinitarians are an answer. If you'd like more information, please write to Father Joseph, Grey Rock, Garrison, Maryland., 21055. Or just mail the coupon."

The placement of an ad for priests in a magazine that carries pictures of nude women generated so much furor - from the Vatican on down - that the Rev. Joseph Lupo, who conceived the idea, swears he never would have done it "had I known."

Playboy may not have been the tactful choice, but the promotional idea was a success. The ad drew 5,000 responses.

In the years since, Father Joseph, the order's vocations director here, has switched his advertising to more conventional magazines and newspapers. Once socially oriented, the ads, which are created by the Lee Blom agency in Baltimore, are now more religious in style.

The energetic Father Joseph is corresponding with 600 potential applicants, including "doctors, lawyers, divorced people and homosexuals." He said they are mainly seeking "guidance."

His latest ad in the Christmas week edition of Time has already drawn 300 responses. The ad showed Christ on a cross. "Since we're inviting you to become a priest, it seems fair to show you a picture of one. We want you to know what you're getting into . . ." it said.

"People are looking for spiritual commitment today," said Brother Victor Scocco, a 21-year-old candidate who has been in the order since he was 17.

The advertising gimmick appealed to Brother Bruce LeBlanc, now 19, who saw one of the magazine ads when he was a sophomore in high school. He put it aside and pulled it out his senior year. It said something like, "there is a young boy in you who always wanted to be a priest." Brother Bruce remembered. The ad was right, and Brother Bruce entered the order's notitiate, or introductory year, a few months ago.

Sine their creation in France by John de Matha in 1198 to buy slaves out of bondage, the Fathers have combined a rigorous monastic life for their own spiritual development with work among society's outcasts.

As the Time ad stated: "Today the world is enslaved in a different way: violence has made prisoners of us all. Today we Trinitarians are sacrificing, working and playing to create a new environment that will end violence. We do it in a hundred different ways, but they are all The Trinitarian Way."

Father Joseph turned to advertising in the late Sixites as Trinitarian monasteries, like most others, began emptying due, in part, to church reforms and extensive experimentation following the Second Vatican Council in 1962-65.

Throughout the U.S., the number of Catholic seminarians preparing for the priesthood fell from 17,604 in 1966-67 to 5,739 in 1975.It is projected that by 1982 the number will be around 4,000, according to the Center for Applied Research in the Apostolate Forum.

At the same time, the Trinitarians have been returning to traditional spiritual practices, like mandatory communal prayer four times daily.

First Father Joseph advertised in Catholic newspapers, but he discovered younger people didn't read them. Next he tried college newspapers and received some response. Major national newspapers brought better results. He adopted the Playboy idea after learning that 80 per cent of college men read the magazine.

Playboy capitalized on the Trinitarian ingenuity. In September, 1975, Playboy placed full-Page promotional ads in several daily newspapers that said: "I read Playboy and found God."

"When the Order of the Most Holy Trinity needed new recruits, they called on Playboy to do God's work," the ad stated.

Father Joseph, 58, has the job of explaining the values of this simple communal lifestyle to inquiring men who have lived in a materialistic society.

What he tries to get across to them is "how much they will have to give. The old expression is 'give up,' but I don't agree," he said. "I think the priesthood can be summed up in one word - generosity."

So, in contemporary terms, he interprets the vow of poverty as "giving of our time." "After all we are not poor," he said. "We live well and eat well. As for celibacy, he said, "I go to bed alone at night, but that doesn't make me alone." Obedience is the toughest vow to accept, he said. "That means to let God and your superiors run your life."

Trinitarian life is family-style, not authoritarian, and their outlook toward the church and society is progressive. The order takes care of the men's food, clothing and shelter. It pays them each $5 a week for spending money as students and $10 after ordination.

About 80 per cent of the income is spent on training future clergy at an average annual cost of $6,000 per student, according to the Rev. David Colella, who is in charge of the 150 priests and brothers in the U.S. Most life."

The men entering now tend to be slightly older than previous eras when they traditionally entered from high school. "We prefer them to have had a job or two and have had their hearts broken at least once," said the Rev. Damon Geiger, the 33-year-old novice master.

"The very young are so idealistic," said Father Joseph. "They're up there on Cloud 9 ready to be martyrs for Christ. I can't spoil their first love. I have to hope when they come in they will mature . . . The older ones, those from 30 to 50, are pretty independent. At that age, you tend to stick up for your rights, look for your pension plans and fringe benefits. Yet, we ask them to come in at least than buck privates."

The vocations director corresponds with the potential candidates for up to two years until they request to see the order or lose interest.

When they come here to the U.S. headquarters, they will find 90 acres of rolling hills, men who eat and pray together and who share household re-income stems from direct-mail solicitations.

Father Joseph says he has benefactors who pay for all his advertising. When he raises some money, he buys another ad.

"The people are out there who want to do something," he insisted. "We just have to go after them."