January is the month for new resolutions, broken resolutions, cold, putting the wrong year on checks, the end of football and . . . sweepstakes.

Sweepstakes offers weigh heavily on a postman's shoulder at this time of year, tantalizing the recipient, holding out hope for a piece of The Good Life, all for the price of a postage stamp.

You may have noticed in your mailbox . . . "Imagine having an extra $25,000 in cash plus $100 a month, every month, for the rest of your life" . . . or, win not one but two Toyotas . . . or, win a vacation home and $5,000 gift certificate and freezer and $2,500 worth of food and '77 Oldsmobile Vista-Cruiser and $5,000 cash, all of it . . . or.

"Six prize numbers plus extra early bird bonus numbers . . . You have 11 chances to win! . . . biggest grand prize ever . . ."

January is the most successful month for direct-mail advertising, including sweepstakes, according to the Direct Mail Marketing Association. (February is second. June is last.) Richard Kane, president of the contest consultant firm of Marden-Kane, Inc., in New York, thinks he knows why.

"A person has been through Christmas and he may not have received what he wanted to get," he says. (Who's going to find a ticket to The Good Life under his Christmas tree?)

"He's been in stores, they've been crowded. Now he's home, relaxing." (In the peace and quiet one finds after the holidays, one sifts the Christmas bills and decides The Good Life has somehow eluded him.)

"Maybe," suggests Kane, "his is the lucky day at the end of the rainbow."

And so, uncounted millions a year, instead of throwing the offers in the trash, sign up for the sweepstakes. Companies usually won't discuss size of mailings, numbers of responses and costs, but it's estimated that at least four major companies mailed out more than 80 million pieces of mail this month to attract sweepstakes entrants.

"Free," say Kane, "is a powerful four-letter word."

"One of our copywriters years ago likened a sweepstakes to a brass band at a revival meeting," says a spokesman for Reader's Digest, which is offering a $50,000 cash top prize in a $450,000 giveaway. "The band is there to get the people into the tent."

Companies that use sweepstakes swear there's nothing offer-filled envelops.

"It's a powerful method of attracting a tention," says Louis Kislik, president of Publishers Clearing House of Port Washington, N.Y., a firm that sells cut-rate subscriptions to magazines and is offering two homes or a life-time income of $125,000 cash as part of a "big all-new $400,000 give-away."

Jimmy E. May, a 36-year-old offshore driller with three children from Many, La., took the cash, then $100,000, that he won in 1975. He then bought his own house - and a lot of other things.

"I bought a four-bedroom, tri-level home with one acre, huge pine trees, a creek, for $30,000, right here in Many," he says. "I got a jeep pickup, then traded it in on a hydroplane racing boat. But I cracked up the boat in two or three weeks.

"Then I traded the engine from the boat and the trailer that came with it for a water ski rig. I got a custom van, carpeted, with a bar, and with red-velvet seats. Then I traded that in for a Mark IV Continental, which I still have.

"I got a little of money left, but not as much as I had. But I got a lot of good memories."

Kislik says sweepstakes are "twice as good" for his company as other contests.

More and more companies are coming to the same conclusion and the result is an ever-increasing number of sweepstakes offers.

A Montgomery Ward Auto Club official says it had its first national mailing for a sweepstakes this month in an effort to increase membership from about 650,000 to 1 million by April. The top prize in the "$100,000 plus Super Sweepstakes" is . . . "Zsa Zsa's (Gabor, who else?) fabulous Roll-Royce."

"What could be more exciting than Zsa-Zsa's Rolls-Royce?" asks the Montgomery Ward Auto Club official.

He says it's one of 17 cars she once owned (all, he says, incidentally, covered by her single club membership).Specifically, it's a 1966 top-of-the-line model currently valued at $61,500 (the promotion says "it was bought at a cost even she is embarrassed to discuss"), that it's been driven about 35,000 miles "mostly by Zsa Zsa, who simply adored driving the luxurious auto."

Reader's Digest says it has given away more than $12 million to 781,514 persons since 1962.

"I won in 1970, $100 a month for life," says a Reader's Digest sweepstakes winner, 69-year-old Vernon Mecham of Casper, Wyo., a retired pipeline worker. "People said it was some kind of trick. The guys I worked with didn't believe it. They said it was some kind of come-along. When I got my first check, I showed them the check. They believed."

Many sweepstakes work this way: A computer selects the winning numbers before the applications are even sent; a recipient returns the form entering the sweepstakes, either accepting the sponser's product or not. The companies say that all entrants have and equal chance of winning, whether they order the product or not. If a winning number is thrown away, a frequent occurrence, the prize is given away by a drawing among losing entries.

Federal Trade Commission officials support those statements. "It's my feeling that there are very few abuses in these sweepstakes," one FTC attorney says.

Company officials say that the numbers of people who decline to accept the product but still wish to be entered in the sweepstakes far outnumber those who take the product, that the "no" winners far exceed the "yes" winners.

An official for the 700,000-member Exxon Travel Club, which is offering a vacation home, automobile, freezer, and other items for its "grand prize," says typical mailing consits of about six million names, and that of the "20 to 25 per cent" who responded by entering the sweepstakes, "96 per cent say no to joining the club." Still, that's a healthy 48,000 to 60,000 new members.

Even the Metropolitan OPera Guild has gotten into the sweepstakes business. The Guild, which has 92,000 members, is hoping to surpass 100,000 members with its "Six Nights at the Opera Sweepstakes." Ten winners get a week for two in New York City and six nights of VIP treatment at the Opera. A "Great Artist at the Met" album is given to 1,000 other entrants.

Guild official Geoff Peterson says his colleagues hit on the sweepstakes idea as a good way to utilize the Guild's message time during the opera's Saturday afternoon broadcasts; listeners can write for an enty blank. Having gone that far the Guild also decided to make a hefty, direct mail pitch.

Peterson admits it's slighty ususual for an opera guild to be in the sweeps. "It's certainly a question we ask ourselves," he says. "But I think it's done tastefully. And it's germane to the public we're offering it to. They're not going to win a car. They're opera enthusiasts who are going to win a trip to the opera."

Behind most successful sweepstakes is a contest organizer, in the case of the Exxon Travel Club, Richard Kane of Marden-Kane. He says he handles "several hundred" sweepstakes of various sizes a year, that most of them work well because "in the fast-paced world all you need it a name and address to enter - it's a quick thing, a now thing." He says a company gets "more bang for the back."

He "supervises the entries and drawing arranges for the judging, communicates with the winners, and in some cases delivers the prizes." Delivering the prizes is not all that difficult if one knows what he's doing; the Exxon club promotion says the winners house will be built "anyplace you say," but is quick to add "in the contiguous 48 United States, as long as a road goes there."

Firms such as Marden-Kane think up sweepstakes and prizes - including many ideas that never get used.

"How about, 'Win all the money in the world!' That's an attention-grabber," says Kane. "It's possible. Just offer $1,000 of each of all the currencies in the world. But morally that's not right. We never tried to sell it to a client."