It occurred to me about two years ago that eating had become the last bona fide sin left in America. That was the year an imaginative sex therapist came out with a book on dieting that contained the memorable line: "Reach for your Mate instead of your Plate."

As someone who had grown up in an era when people were told to sublimate their sexual urges in platters of linguine, I realized that something big was happening. We were actually being told to sublimate our eating urges in sex.

You see, sex was now "healthy" and "normal," while eating was "evil" and "perverted." The same people who read "The Joy of Sex" in public would only eat Reese's peanut butter cups in the closet. The people who were happly after intercourse were guilty after the dessert course.

By now we must all be aware that obesity is the one "Imm-Oral State" of the '70s. Our Sodom and Gomorrah is one in which puffy people sit around washing down cheesecake with quarts of eggnog.

I have heard the same people who talk about alcoholism as a "disease" and crime as a "social disorder" ("I'm depraved on account of I'm deprived") speak of fats as unforgivable. They may express all kinds of sympathy for an amphetamine junkie, but someone who has gained 10 pounds is accused of "letting herself go." Someone who has a new tube around the middle is guilty of having "no willpower."

We judge our figure flaws as character flaws. We are so convinced about the Perils of Pounds, that when a lemon meringue pie is set before our eyes, we label it "Temptation." And when we scrape up the fudge sauce that overrunneth its cup, one of us is sure to say, "Isn't this positively sinful?"

Well, with all this unorganized sin around, is it any wonder that religion entered the picture?

At Oral Roberts University, for example, fundamentalists are so sure that lean-ness is next to godliness, that they cast out of the convenant (and the school) anyone who can't get rid of excessive body fat. Half-a-dozen former students are bringing suit. At the very least they should rule that the university's first name constitutes false advertising.

There are several other groups trying to persuade fat people to repent of their sins. They all seem convinced that the weight on our bodies may keep our souls from soaring, and they preach How to Find God and Lose Weight. (When you see that title in Reader's Digest, remember that you read it here first.)

Among these get-thin evangelists is Frances Hunter, who has written a book called "God's Answer to Fat." No one knows exactly what Fat asked God, but apparently His answer was "Cut Calories."

Another book by Joan Cavanaugh, is called "More of Jesus and Less of Me." Cavanaugh's non-fattening truths read like this: "I can't imagine Jesus coming out of the supermarkets with 12 bags of chips, one for each apostle." The lady is tough to argue with.

In Minneaspolis last week a group called Overeaters Victorious, Inc. formed a statewide network of revivalist diet workshops under the motto (John 3:30): "He must increase, but I must decrease."

The Calorie Conscience Movement has all kinds of ramifications for religion. You can kiss the church cake sale good-bye. Passing the plate is going to have a very different connotation. The notion that the devil lies within is still okay, but he's hiding in all those fat cells, and the work of a good preacher is to starve him out.

All in all, Sinners of America, it appears that the current stairway to heaven is lined with celery sticks. Everyone wants to be Born Again . . . three sizes smaller.