Why is it that people like the Websters and their brethren on the Christian right seem to take all the blame for religious intolerance and blind dogmatism {"What's Wrong With America?" Magazine, July 26}? Nowhere in his otherwise excellent piece did Walt Harrington even hint that liberal -- or''progressive'' -- Christian denominations have been infected by fundamentalism equally as virulent -- and perhaps more dangerous -- than the variety afflicting the Websters.

It's true, the book-burning, backwater Yahoo remains the most compelling symbol of ignorance and intolerance, thanks largely to the acid-tipped pen of H. L. Mencken. But what of another more modern variety of true believer?

What are a Maryknoll nun who swoons over the incendiary rhetoric of every Marxist revolutionary in Latin America; the saviors of the Sanctuary Movement who regularly bump Nicaraguans from the freedom train because only Somocistas would flee Sandinista paradise; the Daniel Berrigans and William Sloane Coffins who canonized Ho Chi Minh and his followers as Oriental Franciscans? Are they not fundamentalists too, as blindly devoted to radical orthodoxy as the Websters are to the literal interpretation of Genesis?

The newer variety of true believer is the ''progressive'' fundamentalist who refuses to let go of shopworn ideologies and tries to cook up "kingdom come" with an oddball concoction of populism, Christianity and a pinch of Marxism for good flavor. Their dogma, like the Websters', has aged gracelessly, yet they continue to suspend their disbelief for the tranquility brought by fundamental faith in the almighty revolution.

Their radicalism, carried out in the name of Christ, scares me more than the simple faith of the Websters.

LARRY DELANEY

Washington