A 16-year-old high school student from Potomac has forwarded to me a "legal" chain letter he received from a California man recently.

The claim of legality is based on the thesis that the recipient of the soliciatation will "buy something of value" when he pays $5 for a one-page report on "How Investors Cut Taxes."

He also pays $20 for 200 copies of the solicitation letter that was sent to him. He gets rich ("up to $5000,000 or more in about 60 days") by selling the copies to 200 people who are as gullible as he is -- provided he can find that many suckers.

Keith R. Bruhl of Falls Church has sent me a post card he received from Tennessee. It says, "You were selected by Contest clearing house, INC. entitling you to receive an exciting 5-day and 4-night vacation offer in fabulous Florida," and it tells you on what day to call a Tennessee number for details.

Apparently Keith called, because the comment he attached to the post card was, "Here is a way to listen to a sales pitch on your own money. Try it and see."

I did try it several weeks ago, Keith. Ann F. Houser of Falls Church had also received one of the post cards, but she was too canny to call. She sent me the card instead.

I am sorry to say that I was curious enough to spend some of The Washington Post's money on a long distance call to Tennessee. I found that we were paying for the privilege of listening to a woman read a long, gushy sales pitch about all the wonderful things I was about to receive without charge. After the telephone bill had mounted for several minutes, she got around to informing me that there would be a nominal service charge of only $49.50 before I could claim my "free" prize.

I said, "Gee, lady, I sure wish I had $49.50 to send you, but I've been out of work for three years and I happen to be flat broke right now. If you could trust me for the $49.50 and lend me a few dollars for travel expenses, I'd hitchhike down and pay you back the minute I got to fabulous Florida. Honest I would." But by that time I was talking to a dead phone.

Let the record show that in the past two months I have been deluged with chain letters and scams of all kinds. It appears to me that for every person who works for a living there are two who sit up all night figuring out ways to get rich quick at the expense of honest toilers. THOSE RTE.66 MARKERS

Several weeks ago, a reader asked about the mile markers on Route 66. He wanted to know where the zero marker is.

The answer is now in, courtesy of Harry L. Meredith of Arlington. He says he traveled the route and learned that "the mile markers start at the juction of Rte. 66 and Rte. 81, near Strasburg, Va." SOME USAGE NOTES

District Liners continue to show a keen interest in the use and misuse of the English language.

James I. Elliott of Clinton thinks writers frequentlyu use most when they mean almost , e.g.: "Most everybody is in favor of the plan. However, Roy H. Copperud's time-saving book, American Usage and Style: the Consensus, summarizes authoritative opinion in these words:

"The schoolgirlish 'most' for 'almost' is called colloquial by Bryant, and Fowler, folksy by Bernstein, and dialectal by Follett. Flesch, however, calls it idiomatic usuage, and Evans sees no objection to it. Random House considers it informal, and Webster gives 'most' as a standard shortened form of 'almost.' American Heritage rejects it. Webster's New World and the Standard College Dictionary consider the usage informal or colloquial. The consensus is that it is good informal usage."

Research consultant Dean Coston didn't like a rather lively sentence that appeared in our paper. The sentence was, "Supervisors hover in their short-sleeved shirts, eight pens to a pocket and a cigarette in each one's mouth."

Coston asked, "What has a mouth? The pens? The pocket? The shirt? Surely not the supervisors -- the reference couldn't go back five nouns, could it?"

Marion Holland noted that when Dr. Frank Miller, our expert on animals, wrote about cat carriers that cut off the air supply to pets placed in them, he told owners that "maximizing" the time a cat must spend in a carrier is important. Apparently he meant "minimizing."

Milt Berliner complained about some wording that left me dizzy the first time I encountered it. It was in a headline over a sports story about slugger George Brett. It said, "Following in Williams' Footsteps but Taking Different Path."

Milt also raised an eyebrow at a criminal in one of our news stories who, we alleged, had been helped to flea . In another story, Milt circled the words serious crisis but didn't trust himself to comment.