If you need proof that mail order is where the action is, consider this: In the past three weeks, I have received no fewer than 75 mail-order catalogs from different companies all across the country.

It is a sign of the times, say trend watchers. Mail-order shopping is booming because busy people who don't have time to go to the store turn to catalogs that can be perused in odd moments and without leaving home.More than $30 billion worth of consumer products are bought via mail order each year. In fact, one company that monitors mail-order, cable TV and other methods of in-home selling has predicted that in the 1990s fully one-half of all general merchandise (including everything besides food, autos and financial services) could be purchased without the customer going to a retail store.

Not to be overcome by this trend, more and more retail stores are also getting into the mail-order business. Whereas a few years ago there were a few large mail-order companies, now department stores, museum gift shops, specialized craft boutiques, and practically everyone else are getting into the mail-order business as well. There are companies that specialize in specific areas; there are companies that offer everything you can think of.

Not that mail order is without risks. You are always taking a chance that the actual product will be what you wanted, based on a picture and few-line description. And there is the time lapse between when you decide you want to buy and when you actually receive the product.

And while most mail-order companies are dependable, there can be foul-ups - involving delayed shipments, lost orders, mixed-up merchandise and sometimes outright fraud.

But, especially at this time of year, mail-order shopping can be a convenient and fun way to do Christmas shopping that helps you avoid some of the crowds.

If you do decide to go on a catalog shopping spree, here are some tips that can help:

-Order in plenty of time. Most companies meet their shipping schedules (provided the merchandise is in stock), but you still have no control over post-office or delivery company jam-ups that occur around the holidays. Check to see if there is a deadline for guaranteed Christmas delivery. If not, allow at least four weeks before you want the gift.

-If time is short, some companies will ship special delivery or express - provided you want to pay for it.

-Buy from well-known firms. If you have questions, check with the Better Business Bureau or consumer protection agency where the company is located.

-Examine the catalog or ad description carefully. Don't rely on picture alone. Be sure to note size, weight, color, contents and other facts about the merchandise you are considering.

-Look for a guarantee. If there is not a "satisfaction guaranteed" provision, be wary of ordering.

-Never send cash through the mail; use money orders, personal checks or charge cards. Remember to add shipping charges when adding up totals.

-Keep a record of your order, including the date sent, a copy of the ad or catalog page, the company's guarantee statement, etc. If you call in your order, record the date and time of your call and get the order clerk's name.

-Check the merchandise as soon at you receive it. If the article is damaged, incomplete or not what you ordered, notify the company immediately. Some companies offer return-mail forms to simplify the task of making returns. The company must reimburse your postage costs if the product was damaged when you received it.

Most mail-order companies depend upon repeat orders and good will to stay in business and are anxious to work out customer complaints. But if you have problems, you can contact the state consumer protection division, action-line reporters such as the Deseret News Do-It Man, or the Direct Mail/Marketing Association, 6 E. 43rd St., New York, N.Y. 10017.

The Federal Trade Commission established a Mail Order Rule that says companies must ship your order within the time promised, or, if no time is stated, within 30 days of receipt of your properly completed order. If you pay by charge or credit card, the 30 days begin when you are charged.

In case of a delay, the seller must notify you when your order will be shipped. If the new delivery date is more than 30 days past the original date promised, you can accept the new shipping date or your can cancel for a full refund. Either way, you must do so in writing. (An easy, no-cost means of canceling must be provided.)

The seller must refund all your money within seven working days after receiving your cancel order if merchandise cannot be shipped within 30 days.

And what if you are receiving more mail-order catalogs and advertising than you want? To have your name removed from mailing lists, write to the Direct Mail/Marketing Association, Attention: Mail Preference Service, at the above address.