Earlier this month The New York Times ran a front-page story on Senator John Kerry's potential problem with the U.S. Catholic bishops ("Kerry, Candidate and Catholic, Creates Uneasiness for Church," April 2).

The article made a now-familiar point that, unlike John F. Kennedy, who had to reassure his fellow Americans in 1960 that his Catholicism would not interfere with the fulfillment of his constitutional duties, Senator Kerry finds himself in the position of having to prove to the hierarchy that he really is a good Catholic.

However, if the bishops, under pressure from the Vatican and/or from their politically conservative constituency in the United States, should decide to slide down the slippery slope of imposing, or even threatening, spiritual penalties for political votes of which they disapprove, they will in the end make it practically impossible for any Catholic to serve in public office.

Why? Because it is a relatively rare Catholic politician who fully adheres to every official teaching of the church.

Those on the religious and political right have no problem with the church's teachings on sexual morality: contraception, homosexuality, gay marriage, abortion, fetal research and so forth.

But such Catholics employ the very same kind of theological spin that their counterparts in the center and on the left do when it comes to the church's social teachings: on social justice, human rights, peace, immigration, capital punishment, governmental aid to the poor, and so forth.

If objectivity and fairness were to prevail, Senator Rick Santorum of Pennsylvania, a strongly conservative Republican, should have no less a problem with the hierarchy than does Senator Kerry --- or any other liberal Democrat who happens to be Catholic.

But therein lies the profound inconsistency of the hierarchy's and the Vatican's approach. They hold the feet of Catholic Democrats and a few Catholic moderate Republicans to the fire on issues that concern human sexuality and reproduction, but give a pass to Catholics on the political right with regard to the vast array of Catholic social teachings.

It was some of those latter Catholics who got themselves into a virtual pretzel-posture trying to reconcile their self-proclaimed Catholic fidelity with papal teaching in the days and weeks after Pope John Paul II came out strongly against President Bush's preemptive war in Iraq.

This particular controversy over Catholic politicians was reignited a year ago January with the publication of a document from the Vatican's Congregation for the Doctrine of the Faith entitled, "Doctrinal Note on Some Questions Regarding the Participation of Catholics in Political Life," which proposed guidelines for Catholic politicians when voting on matters pertaining to the protection of human life.

Significantly, the document mentioned no penalties, including the denial of the sacraments. That punitive course has been advocated by a tiny number of extremist U.S. bishops (and that is the only way they can be described, because almost none of their fellow bishops have stepped forward to support, much less emulate, them).

The leading episcopal proponent of spiritual punishment was recently promoted to the archbishopric of St. Louis, Raymond Burke, formerly bishop of LaCrosse, Wisconsin, where he had made similar threats about denying Communion to Catholic politicians like Senator Kerry.

What these prelates do not seem ever to have learned is the distinction that the late Jesuit theologian, John Courtney Murray, and others had made between the moral law and the civil law.

To have made the moral argument against abortion, for example, is not necessarily to have made the legal argument as well. St. Thomas Aquinas himself had insisted that if civil laws laid too heavy a burden on the "multitude of imperfect people," it would be impossible for such laws to be obeyed and this, in turn, could lead eventually to a disregard for all law.

Moreover, unenforceable laws are worse than no laws at all. And without a sufficient consensus within a society, no law is enforceable. Civil laws, therefore, can demand no more than a pluralistic society can agree upon.

If this is true of society as a whole, it is also true of its Catholic legislators, such as Senators Kerry and Santorum, who are called upon every day to make practical judgments about complex issues.

Which law will best serve the common good, given the moral consensus currently existing within the society? In the purist's mind, it is "all or nothing." In the practical politician's mind, it is "half a loaf is better than none."

If politicians mess up, they can be voted out of office. In the end, it is the people, not prelates, who decide.

Father Richard P. McBrien is the Crowley-O'Brien Professor of Theology at the University of Notre Dame.