I HAVE RECEIVED a letter." said a young woman who can spot a trend when she sees it, "from a fellow I haven't seen for seven years. He's married and has a kid now, and lives in St. Louis, but here came this letter from him after all those years."

She flung her head back and waited for at least three men to say it was hardly surprising a man would remember her well after 20 years, let alone seven.

"My friend Nina also received a letter quite similar from a man she knew ages ago. So did my friend Kathy and so did Marian, all in the last couple of weeks. You should look into it."

For some reason one gets a poor "response asking girls on the street. "Have you had any letters from old boyfriends lately?" and research is not, therefore, complete.

No man I know has confessed to writing old girl friends, and some have made slurring remarks on the theme of thank-God-she's gone.

"In the spring," said the young woman, "you go out and do things, but in the fall you stop to think about them. Besides, this is when the leaves turn such beautiful colors on the trees."

Which naturally, explains everything.

One thinks of these bare ruined choirs where late the sweet birds sang. Doves, as anybody knows, can be ferocious with other doves, but not everyone recalls how beastly other sweet birds can be.

An yet you know, when you stop and think of it, that shamas and dhyals are invariably shipped in individual cages. You put a dozen of them together and only one will remain alive the next morning. These are among the sweetest of all singers, however.

There is a biological basis, in other words, for singers who love to tear their rivals apart, verbally.

Which brings us to an aspect of brotherhood too often ignored: It is not the foreigner who needs understanding, sympathy, civil rights, etc., but the brother.

When families get into war plumage over marriages, it is usually the Montagues and the Capulets, families of equal rank, rather than families from different sides of the jet stream.

In religion, it is easy enough to accept fire worshippers. Zen folk and Druids, but one may often have prejudices against, say, Presbyterians. You will say, if you feel that unreasoning prejudice, they all preach forever and talk about Edinburg. And yet you may feel no resentment at all toward Roman Catholics, Jews, Hellenic Orthodox or even Baptists.

This all bears, surely, not only on social harmony and the correct ordering of justice among citizens, but on the "security," as they call it, of buildings.

Every building nowadays has a guard.

The guard gazes at one's identification and lets one pass. Each day he looks at your card, and of course you are naive if you think he will let you in after seeing you for 20 years. But you show the magic card and you are in the building, safe at last from whatever sinister forces are beating the doors trying to get in, but who, thank God, have no cards.

And yet, the day the building finally is blown to smithereens, we all know it will be Tom or Steve or some fellow who has been around since Ought Four.

The only safety is to have only one of anything - Indian birds, sopranos, presidents, Episcopalians, bassets, writers. More than one and you've got blood to clean up.

The Daughters of the American Revolution are commonly believed to have heroic busts shielded from the noxious fumes of city traffic by a layer of orchids and when they meet in solemn assembly the cliche guest they resolve the nation needs more soldiers and guns and fewer muddle headed treaties.

But of course the image of anything is usually at some remove from the truth, and when the Daughters invited the press, for the first time in 87 years, to attend a national board meeting yesterday, one hastened to go.

"Good morning," said the president general, Mrs. George Upham Baylies.

She walked into the elegant meeting room on the second floor of 1776 D ST. NW accompanied by a group of national officers, and the room of perhaps 70 state regents and other officials rose as she entered. "Good morning," they said back, in unison.

A civil and non committal greeting is a good overture to anything, though some in the visitors' seat were sorry to see that somewhere along the are of time the big orchids have disappeared and - if it is not impertinent to say so - the right foundation for them to rest on.

My Own grandmother, a Daughter of yesteryear, was a three-orchid woman and knew how to order a household.

These modern Daughters look like regular women - a third of the 207,000 members are 18 to 35, it turns out.

"The wider the sash," said Laura Patton, an interpreter of the temple mysteries for the laity, "the more important the office."

So Baylies wore a sash that Victoria herself might have envied when they made her empress of India. Not that she looked Victorian. She would easily have been an investigator of industrial accidents for a large insurance company, or a clothes designer or model for charity benefits (all of which she was been, inf fact), and anyone can tell at a glance she is the sort of wife who never yet has caught the stove on fire or run out of dog food.

"I joined the Children of the American Revolution at the age of 5," she said, "and all I remember is we met on Washington and Lincoln's birthdays and had ice cream and a Punch and Judy show. But I think something must have rubbed off, since I've been in for 41 years now."

She took some reporters to her office, a gracious room with brocade and fuzzy-ball draperies, a gilt mirror with wheat sheaves and garlands, a glided eagle from 2 notable flagpole, and a Scottish Terrier used to strangers.

The dog wears a narrow blue and white silk sash instead of a collar, but in deference to anatomy (Scotties have short necks) it is only the narrow state recent's sash.

The president general's medal was made decades ago by Caldwell, the Philadelphia general since has lived in terror. Baylies said, she might lose it or drop the sapphires out or otherwise fail to pass it on in pristine condition.

Once Baylies coped with the insurance claim of a woman whose hair caught in machinery that fore most of her scalp off, and once she went to a man's house investigating a claim and was rattled to read later in the newspaper that he had a criminal record and had in fact shot someoody BANG. But most of her life she lived in Scarsdale, N.Y. For her term of office she has a suite at the Mayflower Hotel and commutes to New York on weekends - fortunately her husband, a Son of the Revolution (distinct from Sons of the American Revolution encouraged her to accept her office.

The Daughters cannot lobby, she said, but of course they do adopt resolutions, up to a maximum of 12. There was a time the Daughters resolved on so many matters nobody could keep up with them, so now 12 is the limit.

At present, the national policy (expressed through resolutions) opposes any limitation of American arms that would result in an inferior defense position: opposes what it terms the "fraudulent" international anti-genocide treaty; opposes tax reform (as an instrument of socialist-oriented change), deplores the "accelerating decay" of the republic: opposes the "surrender" of the Panama Canal which would complete the "encirclement" of America by Reds; opposes International Women's Year, and the Equal Rights Amendment; opposes national health insurance schemes and universal voter registration (which would weaken the Electoral College system), opposes terrorism and supports the FBI and CIA; and, in general, the Daughters seem distinct from the Weathermen.

"We are a conservative group," the president general said, "I don't know why," she said - members just feel that way.

Nevertheless, Baylies has cut several ceremonial things that used to be said at the ends of reports, to save time, and she hopes the states will open their business up to the process people will stop thinking the Daughters are "old ladies," Baylies said.

Men, possibly for the first time were given sample applications for membership. "I don't think I could qualify," one said, but "well, you might," said a Daughter.

"People do not think of us in the forefront of the liberation of women," said Baylies, "but when the Sons of the American Revolution would not let us join, we started the Daughters in 1890, and these headquarters are the largest group of buildings in the world owned and maintained exclusively by women."

Men noticed their application form was stamped in huge letters, "Sample." They wouldn't really let you in.

Still, the Scottish Terrier general and all the women were as friendly as if one had been a Daughter, and if a flaming liberal femal descendant of the Revolution wanted to join and didn't mind being a little conspicuous, no reason she couldn't.