As a pastor seeking to lay a guilt trip on his flock, Cardinal Humberto Medeiros of Boston is a flop. A few days before the congressional primary elections in Massachusetts last week, the two million Catholics of the Boston archdiocese were urged by the cardinal to vote against candidates who favor federal funding for abortions.

Saying that abortion is "an unspeakable crime" and that these are "blood-drenched" times, Cardinal Medeiros wrote in a letter printed in his diocesan newspaper that "those who make abortion possible by law -- such as legislators and those who promote, defend and elect these same lawmakers -- cannot separate themselves totally from that guilt which accompanies this horrendous crime and deadly sin."

A large number of the faithful -- apparently a theologically alert group that believes God, not the cardinal, is the best judge of guilt -- voted for Barney Frank and Rep. James Shannon, candidates "who make abortions possible by law." The supporters of Frank -- a state politician who seeks the seat being vacated by Rep. Robert Drinan, the priest pushed out of Congress by the Vatican -- believed that his overall record was sufficiently liberal and humane, regardless of his stand on one particular issue.

It is hard to see how the Medeiros blast brings the discussion further along. He is now aligned with the hit list approach to politics, so favored may have been a more effective vote-getter for Frank than the craftiest of precinct captains. Reporting on the backlash to Medeiros' letter. The Boston Globe quoted one citizen of unbossed spirit: "I wasn't going to vote until he [the cardinal] sent out the letter; then I voted for Barney Frank. And I'm Catholic."

In using his moral voice to tell people how to vote, Cardinal Medeiros can't help confusing outsiders. One muddle is this: if abortion -- "this horrendous crime and deadly sin" -- is so evil, why doesn't the church really exert its strength and excommunicate its members who refuse to obey the official teaching? I am opposed to abortion, but if that issue alone dictated my views about politicians, I would have been angered that Drinan wasn't thrown out of the church, not merely Congress. The Vatican could get a list of Drinan's Catholic financial supporters and excommunicate them too. In Congress, other guilty ones who voting records on abortion are a bit too sinful would also go: Irish Catholics like Sens. Edward Kennedy and Patrick Leahy.

Such a purge would be a new inquisition.To hear some of the noisier opponents of abortion, burning a few of these heretical "baby killers" at the stake wouldn't be too far beyond what they deserve.

By trying to put a move on liberals like Frank and Shannon -- both were opposed by anti-abortion conservatives -- Cardinal Medeiros keeps alive the illusion that the abortion debate is divided along the lines of liberal v. conservative, Catholics v. non-Catholics.

This has never been the case, and even less so now. One of the most persuasive arguments in favor of protecting the rights of the pre-born has been made by Dr. Bernard Nathanson, a non-religious and liberal Jew who for 10 years was a leader of the pro-abortion movement. As an obstetrician, he presided over 60,000 abortions. In his 1979 book, "Aborting America," which details his change in thinking, Nathanson asks the questions that are regularly raised by moral theologians, whether Catholic Protestant or Jewish: "Parents may not abandon their children; why should they be encouraged to abandon their children-to-be? One race ought not exploit another; why should the already-born be allowed to exploit the not-yet-born?"

Nathanson's argument, which I have yet to see refuted, is based on what he calls "the obvious scientific conclusion" that the fetus "is demonstrably an independent human entity [life]." This, he says, "is a humanistic philosophy drawn from modern biological data, not from religious creeds."

Those like Cardinal Medeiros who speak out against abortion based on their creeds have an obligation not to squander the gains and support that have been won by non-Catholics and non-conservatives who are "pro-life" on this issue, as well as all others. Aside from alienating the citizen quoted by The Boston Globe -- and probably thousands more like her -- the Medeiros letter reinforces an image of the church trying to impose its morality on public policy -- or, in this case, public figures like Barney Frank. It is poor strategy and shabby morality.

Are we to believe that any Catholic who voted for Frank must now take his guilt-ridden soul into the confessional and say, "Bless me, Father, for I have sinned. I voted for Barney Frank."?