Q.A gentleman acquaintance of mine, a weekly guest for four years, has been barred from our house by my mother, who is displeased by the length of his hair.

What exactly can a mother do about the hair length of someone else's child? After stating her opinion, how far can she go in enforcing it? She has offered to drive him to the barbershop of his choice.

The objection is merely to the hair -- and other than the length, he takes very good care of it -- as the gentleman in question does not behave in the manner usually associated with long hair.

A.When Miss Manners' dear late Aunt Grace was a girl, some years ago and then some, her father barred the door to one of her beaux because he wore a gold earring. He allowed another beau, conventional and shy, to continue calling. The first was Ezra Pound and the second D.H. Lawrence.

Aside from the fun of literary name-dropping, Miss Manners recounts this story to alert parents that you never can tell. Had the vigilant papa but known how these two would turn out, he would still have pitched the eccentric young man, of course, but would have taken care to send the presentable-looking one sprawling after him.

Miss Manners does not deny that appearance is symptomatic of social attitude, only that it is difficult to read, especially in the young. In your case, the young man's supposed defiance of polite society, in wearing long hair, is extremely mild. One might even consider it nonexistent, as the current era admits a greater range of socially acceptable hair-lengths than most.

Miss Manners disagrees with your mother about barring the door on such slight provocation. That is her privilege, however -- but it is her only privilege.

Even telling the caller that his hair is offensive is a violation of etiquette. One may only tell one's child and allow the child to pass along the explanation, presumably mentioning that she disagrees.

Attempting to enforce her own standard is a really serious violation. For all your mother knows, the young man may be dutifully copying the style of his father.

Q.My husband of 50 years passed away, and I hope you can help me do the correct thing. I don't know what the rules of mourning are. I'm old-fashioned and want to wear black for a year at least. The way I feel now, it might be forever.

Do I have to wear stockings all summer? Around the house and during the day? I would wear them if I went out in the evening with the family.

A.Do not imagine that Miss Manners is attempting to discourage you from assuming formal mourning when she informs you that it is no longer the custom. It was a very good custom, serving to protect the bereaved from ordinary social treatment when they might be unable to handle it emotionally, and Miss Manners is willing to help you adapt it for modern use.

But we must understand the spirit. Mourning signifies that one is temporarily withdrawing from normal cheerful society because one does not feel up to it. Using the trappings of mourning to show off one's feelings, or to dampen the spirits or activities of others, was always considered vulgar.

One does not therefore wear obvious mourning to an office, or as casual wear, or to any social event. This was not formerly a problem, as a woman in mourning simply stayed home, and a man's black hatband or black suit was fairly inconspicuous.

A widow wore deep mourning (black clothes of plain, matte finishes, with a widow's bonnet and crepe veil) for a year, and then "second mourning," including black ribbons, jet ornaments and touches of white, gray and mauve.

Let us adapt this to modern dress.

Veiling should be worn only to shield the widow's face at the funeral itself, where Miss Manners prefers it to the current substitute, sunglasses, which look incongruously jaunty.

To an office, or when following the normal business of life, wear plain black clothes, with just enough white so that uninformed people don't jokingly ask who died.Miss Manners would not consider black stockings necessary, any more than you need order black-bordered handkerchiefs. But as you do not wear mourning casually, you need not worry about events to which you would go stockingless, anyway.

If you do attend social events, do not wear mourning, although you may use black, gray or mauve to avoid dressing gaily. Around the house, unless you have visitors, it doesn't really matter. Remember that the purpose of mourning is not to demonstrate loyalty to your late husband but to remind others of your delicacy.

Therefore, Miss Manners begs you not to set a time limit. Society no longer recognizes one. Let us instead hope that the time will soon come when, although still bereaved, you feel up to resuming normal life.