LITTLE HAS HAPPENED in Washington during the past several months to make my spirits sour as much as Sen. Jeremiah Denton's assurance that our national troubles can be traced to the prevalence of premarital sex.

Until now, I had been consumed with guilt as a consequence of my past involvement with American foreign policy. The post-Vietnam malaise, inflation, the Cubans in Angola, the boat people, OPEC's greed, the drug problem and the defense gap were all traceable, in my own tortured thinking at least, to various memoranda, briefing papers and communiques I had written over the past 25 years. But Sen. Denton has freed me from my shackles.

I wish, though, that Denton had quit while I was ahead. But, no, to prescribe a cure that may make my release from self-flagellation but momentary: The government, he suggested, should encourage teenage chastity.

The senator's idea is unique in the sense that it comes at a time when a prime aim of our present government is to get off our backs. But Denton is actually carrying on an old tradition. Some may still remember Rep. Andrew Joseph Volstead of Minnesota, who was convinced that all the ills besetting America could be laid to alcohol. And so, in 1918, over President Wilson's veto, the Volstead Act was passed, and a year later the 18th Amendment was ratified and Prohibition was born. For many years after, people drank in cellars instead of their sitting rooms.

Mr. Volstead's intentions were lofty, but even the federal government could not successfully legislate against sin. Ask Mort Mortimer. He was President Harding's bootlegger and delivered his merchandise right to the White House door.

Demon Rum is not the only villain our lawmakers have tried to subdue. In the year of Rep. Volstead's triumph, Virginia prohibited a woman from wearing a gown which "showed more than 3 inches of her throat." And the State of Ohio, in the same year, proclaimed that "any female over 14 years of age is prohibited from wearing a skirt which does not reach that part of the foot known as the instep." Three years later, the State of Utah threatened a fine and imprisonment for women appearing on the street with skirts "higher than 3 inches above ankle."

In 1925, the City of Norphlet, Ark., passed this ordinance: "Section 1) Hereafter it shall be unlawful for any man and woman, male or female [sic], to be guilty of committing the act of sexual intercourse between themselves [sic] at any place within the corporate limits of said town. . . . Section 3) Section 1 of this ordinance shall not apply to married persons as between themselves, and their husband and wife [sic], unless of a grossly improper and lascivious nature."

With all respect to Sen. Denton, chastity begins at home. Neither he nor the local U.S. chastity administrator would be a good surrogate for parents, teachers or ministers. Experience should have taught us that Washington, D.C., is a poor base from which to wage war against sex. It is a much better place, it seems, from which to pursue the wretches who lost china, etc., etc. But until the senator's noble experiment has run its course, I will be able to sleep the sleep of the virtuous; to my certain knowledge, I have eschewed premarital sex for four decades.