Q. I am a single woman planning an open house in celebration of my 40th birthday. The event will span an afternoon and evening in my medium-sized, four-room flat.

My wish is to invite a wide variety of people who have played significant roles in my life. They range from radical lesbian feminists to macho male chauvinists, militant peace activists to National Rifle Association members. Also, some of the guests, for perhaps obvious reasons, no longer speak to each other or choose not to publicly acknowledge their acquaintance.

I have considered inviting different groups of friends at different times, segregating those who might be antagonistic to one another. However, this seems to imply that my guests are incapable of conducting themselves in a civil manner.

How can I promote a congenial gathering for my guests and myself?

A. For social purposes, you have only two types of friends: those who can be trusted to behave politely to everyone they meet under a friendly roof, whether they happen to share their opinions or not, and those who can't.

While appreciating your reluctance to advertise the fact that you consider some of your friends to be in the latter category, Miss Manners gathers that such, indeed, is the case.

Those people must be kept from meeting anyone they might attack, and known enemies should not be invited to the same party. Preference is given either to the more amenable person or to the one you think is right.

For a small party, one does try to choose people who are likely to find one another agreeable -- which is not always the same thing as those who are likely to agree with them. But at a large gathering for a particular occasion, people are supposed to be too interested in what they have in common -- affection for you on your birthday -- to worry about propagandizing.

Miss Manners suggests you invite everyone you trust to behave (entertain the troublemakers separately, if you think them worth the trouble) and bubble over emotionally about how your dearest friends have far different ideas but share their basic goodness and worth.

Then they can all wander around to find compatible souls with whom they can exchange looks of "Aren't these other people outrageous?"

Q. My niece, who had a lovely wedding, sent out thank-you notes with only her name signed. No mention of the groom at all. Only her name and address were on the envelope.

Several friends have called, wondering why. My niece said she went to the library and found that this was the correct way today. I always received thank-you cards with both names, but she claims this is not correct.

A. Your niece is only half right. She did, indeed, read that a letter -- as opposed to an invitation or a card -- can only be issued by one person and that therefore only the name of the bride (or bridegroom) is signed. (This is not a change for "today"; this has always been the rule.)

But she overlooked the fact that the letter writer for a joint present is performing the job of speaking for the other half of the couple. "We" should be used in all expressions of appreciation, and a sentence such as "Kevin is crazy about the lamp -- orange is his favorite color" is obligatory.