In earning high television ratings last week, "The Thorn Birds" also gave high visibility to a question long debated as a private matter among theologians: marriage and the priesthood. The love story between Father Ralph and Meggie had the bedroom scenes necessary for prime-time success. Instead of sex and violence, "Thorn Birds" offered sex and God. It was, after all, Holy Week.

The steamy side became the bright side when ABC, with a sharp news sense, serviceably focused the issue by widening the context. From David Hartman in the morning to Ted Koppel at night, the network gave air time to the debate on clerical celibacy by interviewing everyone from married former priests to a cardinal.

The newsworthiness is the manpower problem within Catholicism. With 50 million members in the United States, it is the nation's largest denomination. It may also have the largest personnel crisis.

At last November's bishops' meeting in Washington, when the media descended in hordes to cover the hierarchy's nuclear disarmament statement, the more startling--but unreported--news was found in a paper delivered by Bishop Nicholas Walsh of Seattle.

He spoke of "the depletion of our ranks": only 4,000 seminarians currently studying for the priesthood (down from 17,000 in 1962); a median age of 52 for priests; a projection of only 25,000 active priests in 20 years (as against 59,000 today); more parishes being unstaffed by resident priests; an increase in requests for early retirement. Walsh concluded that "our priests are suffering from stress, burnout and frustration."

The bishop wondered what all this said about celibacy. Shortly after, a study commissioned by the Knights of Columbus offered an answer: 27 percent of the Catholic men between 18 and 30 would seriously consider the priesthood if marriage were allowed. Almost immediately, the church could transform a vocation crisis into a vocation boom--if it made celibacy optional.

Such a change in church policy seems remote. In 1967, Pope Paul VI decreed in an encyclical that clerical celibacy would remain. Pope John Paul II agrees: Single is best.

If the church were a democracy, not an autocracy, a married clergy would be as routine in the Latin rite as it is in numerous Eastern and Oriental rites. As far back as 1966, a survey of 3,000 American priests revealed that 62 percent favored optional celibacy. Ninety-two percent favored the welcoming back of married former priests to the church.

A common argument in favor of bachelor priests is that total dedication to God isn't possible if attention also must be paid to a wife and family. On ABC's "Nightline," Cardinal John Krol offered several anecdotes to bolster this claim. But what of the countless Protestant, Orthodox, Jewish and Moslem married clergymen in America whose devoutness and service are as transcendant as any unmarried priest's? It has never been proven that the absence of married sex is automatically conducive to either holiness or self-giving.

Long before "Thorn Birds," which is a tale of a priest overcome more by ambition than sex, American fiction had the stories of J.F. Powers. His pastors and curates never thought of women, except when it came time to hiring maids and cooks for the rectory. Their devilishness ranged from the conniving for ecclesiastical promotions to the love of country clubs.

The Vatican's firmness for mandatory celibacy affects more than Catholicism. It is a major block to the unification of Christian churches. Other denominations rightly ask: What is the scriptural basis for required celibacy? There is none. Ten of the 12 apostles were married men who in turn ordained younger married men to carry on.

The current debate, whether in the public forums of news programs or in church councils, is not about eliminating celibacy but merely making it optional. Marriage would remain what it is for any person: a choice.

A practical effect would be a reversal of the church's personnel crisis. A management consultant could figure that out. The greater benefit would mean the enrichment of countless lives: the thousands of married former priests who are eager to return to the service of the church, the young who see marriage as an enhancement to a sacramental ministry.

The church's contributions to American society are enduringly valuable. Not to allow its own members to contribute to their own church is to hurt everyone.