A feisty Texas clergyman-journalist, frustrated in his challenge to debate Moral Majority leader Jerry Falwell by a scornful refusal from the fundamentalist pastor, has claimed victory "by default" in a Mailgram denouncing Falwell in biblically coded epithets.

"I readily understand," the Rev. Spurgeon M. Dunnam III wired Falwell, "why you would rather decline my invitation and lose by default rather than to risk having the truth of Matthew 7:15-17 demonstrated before an audience including many fellow Christians."

Matthew 7:15-17 reads: "Beware of false prophets, who come to you in sheep's clothing but inwardly are ravenous wolves . . . "

Falwell hurled a few barbs himself in his Mailgram refusing to debate with the editor and general manager of the Dallas-based United Methodist Reporter. "I don't feel you represent a viable segment of Christendom," the Lynchburg pastor told Dunnam. " . . . . Only a small fraction of the more than 10 million Methodists in the United States receive your paper and even smaller percentage, in my opinion, endorse your liberal philosophy. Most Methodist sic stand for traditional moral value and believe the Bible is the word of God."

Dunnam's independent weekly has a national circulation of 540,000, by far the largest paid circulation of any religious publication in the country.

In United Methodist circles, Dunnam, 38, is viewed as a middle-of-the-roader theologically who frequently criticizes denominational programs for being too liberal. He has on occasion faulted church leaders for failing, in his view, to adhere sufficiently to the Bible in developing programs and policies.

Dunnam challenged Falwell to the debate last month, he said, because of "a conviction that the Moral Majority has come to epitomize a type of political activity draped in religious terminology which I consider fundamentally at odds in many respects with the gospel of Jesus Christ."

In rejecting the call to debate, Falwell wired Dunnam: "A debate will not resolve the basic differences between us. I believe in the verbal inspiration and infallibility of scripture. You do not. I therefore oppose abortion, you do not. I want to eliminate pornography. You did not. A debate would not change your mind or mine."

Dunnam demanded "a public apology for having both libeled and slandered me" with the soft-on-pornography charge. "My position vigorously opposing pornography is a matter of written record, consistently stated numerous times, in numerous ways, over a period of 12 years," he countered in his response to Falwell. "You should be thankful that I take seriously I Corinthian 6:1,7," St. Paul's admonition to Christians to settle their differences out of court.

Nelson Keener, administrative assistant to Falwell, told the Dallas Morning News that "we don't feel a debate would be profitable." It would not be good "for the good of the Gospel" for two clergymen to disagree publicly, he said.

The Texas churchman denied that he was involved in a crusade against the new religious right, even though the challenge to debate Falwell is his third or fourth go-round with this segment of Protestantism. "I tend to think it would be a mistake" to launch such a crusade, he said in a telephone interview. "I think an editor, if he does his job, has a crusading function, but it shouldn't be that narrow."

Dunnam, who is no stranger to criticism from his readers on both the right and the left, said his mail and phone calls have been running "about 25 to 1" in support of his challenge to Falwell.