Post reader Helen I. Francis should have included astrology in her accurate assessment of the much publicized "harmonic convergence" as a "bunch of cosmic, cultic horseradish" {Free for All, Aug. 22}. But since when can a self-anointed astrologer give lessons in the true science of astronomy to a professional astronomer?

Leroy Doggett of the U.S. Naval Observatory might have pointed out that the charts and calculations of astrologers bear no relationship to the true orbital positions of the planets but like "psychic" predictions are couched in the broadest possible terms in order that wide interpretations may be made.

Among hundreds of totally negative test findings made over many years, I might remind Francis of the massive scientific study of French citizens made by researcher Albert Gauqulien, who compared the astrological charts of 50,000 persons with their lives over a 10-year period subsequent to charting only to find no correlation at all between lives and predictions.

A more recent test involving 30 American and European astrologers alleged to be the best in the business was conducted by Shawn Carlson at the University of California. The tests utterly failed to prove the contentions of the participating astrologers that they could predict futures by reading so-called natal charts for 116 clients. As was to be expected, the astrologers had their cop-outs ready, calling the tests biased -- in spite of their having approved all test criteria beforehand. Such is the tenacity of the true believer.

The well-known psychic debunker and professional magician James Randi, writing in his book "Flim-Flam," labels astrology one of the oldest claptrap philosophies known to mankind, with more than 20,000 astrologers currently taking money from credulous suckers. I also note that the well-known 20-year veteran astrologer John Townley was quoted in Astro-Talk of May/June 1986 as saying that 90 percent of all astrologers are charlatans.

Those who are seeking the "great truths" will not find them in the sort of metaphysical hogwash being peddled by such as Jose Arguelles, Shirley MacLaine or guru Maharishi Mahesh Yogi. But they may enlighten themselves through a devotion to the sciences, instead of allowing themselves to be driven over the cliff like human lemmings by self-anointed prophets out for the fast buck.

-- William H. Watkins Not So Swell Since television (including network news anchors), radio and popular magazines are failing miserably in their responsibility to maintain standards of good grammar, the ultimate defender of good English usage in this country is the newspaper editor.

Because of its large, broadly based readership, its acknowledged influence on public opinion and its stable of prominent writers, The Post should be a leader in the defense of good grammar and should be setting a consistently good example.

For this reason, I hasten to call your attention to examples of bad grammar that should never have survived the editor's pencil in recent issues.

1. Sports: "Wade said . . . there had been a misunderstanding between he and Nevin. . . . " He is the object of a preposition; the correct word to use in this position is him.

2. Entertainment/AP wire story: ". . . the high-rated daytime serial." I suspect you might agree that highly rated would be the better choice.

3. Sports, again: ". . . Kleine has a swelled right knee." I hope you'll agree that using a swelled instead of a swollen is not so swell, even if some dictionaries may indicate both forms of the participle are correct.

I could continue, but I won't. I'll simply close by pointing out that many of the people who read your newspaper every day -- especially the thousands of young people who read the sports and entertainment pages -- learn from what they read. If, unsuspectingly, they encounter poor grammar, they'll soon be using that same bad stuff when they talk and write.

-- Arthur P. Brigham Guadalcanal, Not Guadalcanal Yes, the dropping of the final e in employee bothers me. And, yes, I find your punning headlines atrocious. Allow me to point out another annoying Post habit:

It's the Achille Lauro, not the Achille Lauro; Challenger rather than Challenger; and Guadalcanal instead of Guadalcanal.

The Post's practice of not italicizing ships' names lessens their majesty and makes it easy to lose the name in the paragraph.

I was always taught that such names should be italicized. All my style books agree.

What's the problem here? -- Scott P. Cook They Don't Have X-Ray Vision Sen. Robert Byrd and Gov. Gerald Baliles may be noteworthy politicians, but they'd have to be supermen to see the view from Old Rag Mountain described in The Post {Metro, Aug. 16}.

Old Rag stands alone just east of the chain of mountains known as the Blue Ridge and rewards hikers with commanding views of the Hughes River Valley and the Piedmont Plateau. The Shenandoah Valley lies 10 miles west, beyond the Blue Ridge. It is hidden from the eyes of mere mortals who, alas, do not have X-ray vision. -- Jeff Bonar