DEAR MR. MELTZER: We live in a nice building in an excellent section of the city. Lately we have had several unpleasant and unfortunate incidents occur right in our apartment house.

Last week an elderly neighbor of ours was mugged in the hallway right outside his door while he was looking for his key. Several weeks ago a girl was grabbed in the garage when she went down to get her car. Luckily, another tenant came along and scared the attacker off.

My husband and I are really nervous. We're middle aged and don't want any trouble. We've noticed that the doorman isn't always on duty when he's supposed to be. And the garage attendant is usually asleep in his little cubicle whenever we go down for our automobile.

Who can we complain to? We've never set eyes on our landlord. We just pay our rent to the management.

ANSWER: The person ultimately responsible for the security in your building is the landlord. There are states and cities which have specific laws requiring the landlord to install anticrime devices.

The landlord cannot overlook conditions which will increase the danger of a tenant being robbed, attack or otherwise injured. If he does, he can expect to be faced with the consequences of an expensive lawsuit.

When something occurs in your building which threatens the security of the tenants, the landlord or management should be contacted at once.

DEAR MR. MELTZER: We're buying our first house, and are we nervous! All of our friends keep warning us about this and that until we're completely confused.

One of the things troubling us is the question of settlement costs. Is there any reason why there should be such a disparity among them? What should we look out for?

ANSWER: When your lender prepares your written application for a loan, he is legally required to give you a copy of a HUD information booklet. He must supply it to you within three business days after the application has been filed.

He must also provide you with estimates of settlement charges you are likely to incur.The final costs may not be exactly the same, due to changing market conditions, etc. Don't be hasty and be careful of your choice of a settlement firm.

DEAR MR. MELTZER: It may sound foolish to ask about weatherstripping while it is still warm. But it won't be long now before the wintry winds will blow, and so I'd better get started.

Is it possible for me to install weatherstripping myself, or must I hire someone to do it? I am anxious to conserve energy, both out of a feeling of love for my country and love for my pocketbook.

ANSWER: Metal weatherstripping is the best you can get, but it must be installed by a professional. Window sashes must be removed, special grooves cut, and the sash must be carefully refitted before replacing.

If you are set on doing the job yourself, there are other kinds of weatherstripping which you could install yourself. There are kits available at hardware stores which have enough weatherstripping for one door or window. Weatherstripping can also be bought by the foot.

If you have never done this before, self-adhesive weatherstripping is available in a wide variety of materials.