Three District Liners have already written to complain about last Sunday's "Prince Valiant" comic strip, and I'm sure more letters are being penned even as I write these lines.So, to save you the trouble of writing, let's get this unhappy business over with quickly.

There was a grammatical error in the strip on Sunday. I dislike writing about it because Hal Foster, "Prince Valiant's" creator, author and artist, is the grand old man of cartooning - definitely not the kind of man one enjoys criticizing.

He has been chronicling the prince's adventures for 42 years. If my arithmetic is sound, Foster is now 86 years of age. Yet his draftsmanship and attention to historical detail seem to improve with time. Unfortunately, however, on March 26 his continuity said, in part, "Val guesses they regard he and his family as infidels."

Remove "and his family" from that sentence and the correct usage becomes obvious. "Val guesses they regard him as an infidel." And when more than one person is involved, the correct wording is, "Val guesses they regard him and his family as infidels."

The same point is illustrated in the misquotation, "Let he who is without sin cast the first stone." The sentence is usually translated into English as, "He that is without sin among you, let him first cast a stone at her." But if you're going to paraphrase it, at least do it grammatically: "let him who is without sin cast the first stone." Let him do it, not let he do it.

For the record, be advised that the first three letters to arrive on this subject were from C. M. Stott, Saul J. Mindel and Anne Donaldson. Mrs. Donaldson was the only one of the three to score a double.

On the day after the error in "Prince Valiant," the "Archie" strip tried to make a job about a skiing accident. "He shouldn't have tried that; he's accident prone," a girl said as she and a friend entered a hospital to visit an injured lad. The final panel showed them entering the sickroom where the skier was bedded down, on his back, with his leg in a cast. And in the dialogue balloon we read, "Yes - he had an accident and now he's prone." Seven years ago, Anne recalled, District Liners pointed out that a man on his back is supine. A man lying on his stomach is prone.

"Incidentally," Anne adds, "I notice that the cartoonist's name is missing. No one wants the blame, I suppose."

No, Anne, there's another reason. "Archie" is turned out by a committee, not by one person. That's why it doesn't carry the name of any single author.

As so often happens when a project is assigned to a committee, "Archie" failed to develop the zing and pizzazz an individual might achieve. Many Washington Post subscribers didn't bother to read it.

This was of great concern to our editors because "the funnies" play an important role in building newspaper circulation. Just as TV officials study the ratings and juggle their schedules accordingly, editors who decide which comics to publish are very sensitive to public opinion. They must keep themselves posted on which strips are rising in popularity and which are fading into disfavor.

And the sad truth about "Archie" is that its popularity with out readers has now sunk too low. So "archie" will be dropped next week, and a new strip, "Superheroes," will be added.

Mary Lou Beatty, the assistant managing editor paid to worry about comic strips and also the unfunny things that appear in our comic section, tells me "Superheroes" is very popular in other cities. So she has bought the Washington rights to the strip, and we will soon have a chance to judge whether it lives up to its advance notices.

If it doesn't, Mary Lou will probably waste little time in replacing it with something better. In private life, she's a gentle person. But when it comes to sending an unpopular comic strip to the guillotine, she's as quick as any editor to snap, "Off with its head."

Sorry to see you go, Archie, but making people laugh is a grim business.