Catholics for a Free Choice was delighted that The Post reported the findings of our recent national poll, which found, among other things, that American Catholics are deeply disapproving of the U.S. bishops' involvement in abortion politics {news story, Oct. 26}. But one thing troubles us. While our poll was conducted and the results released in a manner conforming with the customary professional standards required of scrupulous polling surveys, another poll cited in the story was given the same credence as ours even though no supporting documentation was cited. And none, I suspect, was provided by the source, the National Conference of Catholic Bishops.

The release of our survey was accompanied by all pertinent supporting documentation. Every question in the poll was included in our announcement. The cross tabulations were made available. And of course, the methodology was described. We even had a representative from KRC Research and Consulting, the national firm that conducted the poll, attend our press conference to answer any questions about the survey itself.

On the other hand, the NCCB has provided no similar data to justify the statistic it provided The Post. We are left to wonder about the bishops' poll. What was the sample size? What other questions were asked? Who conducted the poll? When? Where? And most important, why was there no attempt to explain why this statistic (claiming that 82 percent of "church-going Catholics" oppose abortion except in limited circumstances) differs so markedly from dozens of independent polls conducted on this subject?

If we are expected to take the NCCB figure seriously, we need to know the whole story. Yet the NCCB has released no supporting data and only a few selected poll results. If the bishops' poll was meant to be private, then none of the results should be quoted in news stories. If it was meant to be public, then let's see the whole poll.

The bishops themselves know that only a small minority of Catholics agree with the church hierarchy that abortion should not be permitted under any circumstance. Why else would they pay $5 million to the nation's largest public relations firm to repackage their anti-choice message?

FRANCES KISSLING President, Catholics for a Free Choice Washington