US home appliance industry having spin-cycle sales pace this year; Customers happy, too, as prices hold; but investors may have missed cycle

Beneath the brilliant yellow roof of a Sozio's appliance outlet here, sales manager Sam Ranallo sits quietly tallying receipts. ''Yeah, it has been a good year. The last couple have,'' murmurs Mr. Ranallo - with the nonchalance of a card player admitting to a ''fair'' hand while holding four aces.

In fact, big-ticket home appliance sales have soared. ''This will be a record year - our best year since 1973,'' confidently predicts Marian Johnson, spokeswoman at the Association of Home Appliance Manufacturers in Chicago. For the second year in a row, the industry is heading toward total annual sales gains of more than 20 percent.

The microwave oven, a rarity during the last appliance boom, is today's hottest-selling item. The electronic sizzlers account for one-fifth of all major appliances shipped. And this year, shipments are up 60 percent over last year.

''The changing American life style'' (more single and married working women) is cited as one factor whetting microwave demand. Also, a blossoming mass-market audience has opened up as Asian producers join in and push prices lower: Some ovens now sell at $150.

Although sales of the larger appliances have tapered off in the last month or so, microwave sales are expected to continue strong through the holidays and into next year. By 1986, manufacturers predict, about half of US households will have one - up from 33 percent last year.

The good news for the consumers is that, overall, prices on most major appliances (refrigerators, dishwashers, ovens, and laundry machines) have sagged slightly. And they aren't expected to increase much, if at all. As the sales pace has eased, competition is heating up in this already highly competitive industry. ''Profit margins are going to get squeezed, so there will be some need for price increases,'' according to Charles Ryan, vice-president of fundamental research at Merrill Lynch, Pierce, Fenner & Smith, the brokerage firm. But no manufacturer wants to sacrifice market share, so the price increases next year are likely to be small - perhaps 1 percent, Mr. Ryan says.

Price, however, plays a less important role in buying decisions than back in the mid-'70s, say analysts. Customers are likely to focus more on quality and special features. ''They come in with a copy of Consumer Reports tucked under their arm,'' says Sam Ranallo at Sozio.

Reliability is essential, but manufacturers are trying to match products to the needs of ''today's changing life styles,'' as well as inject a little pizazz into their lines.

''The appliance industry is very boring: A white box is a white box is a white box,'' admits James Krueger, director of marketing at Admiral, a subsidiary of Magic Chef Inc. For its part, Admiral introduced a ''flash freeze'' freezer this year that gives longer storage life to frozen foods.

And all the manufacturers are melding the basic appliance with silicon circuitry. For instance, industry leaders General Electric and Whirlpool have top-of-the-line refigerators that beep when your child grabs a snack and leaves the door ajar. Both include a digital display panel to alert you to mechanical problems. And the Whirlpool model has a light that tells you when to dust the condenser.

Other electronic gizmos include ''programmable'' dishwashers and laundry equipment. One GE microwave now has an electronic nose that sniffs for the proper aroma to tell one when the roast is done.

Despite manufacturers' claims for added convenience, analyst James Magid at L.F. Rothschild, Unterberg, Towbin calls most of these gadgets ''trivial.... Whirlpool should design the condenser so you don't have to vacuum it.''

This week the Maytag Company introduced a full-size stacked washer and dryer combination with a single digital control panel. Mr. Magid calls it ''a spectacular product.'' Until now, if floor space was limited the only option was to buy a stacked unit of less than full capacity. But Magid says the ''real technological innovations will be in the area of brushless direct-current motors.... In the next two or three years, motors will use less energy and be more reliable.''

Another selling feature touted by GE and Whirlpool is the customer repair manuals now being published. ''There's been a definite trend toward more people doing their own repairs,'' says Whirlpool's Joy Schrage. In 1976, 15 percent of the people calling on Whirlpool's toll-free 800 number sought repair or installation instructions. By last year, 34 percent were seeking repair advice.

''Some are do-it-yourselfers for economic reasons, others because it's more convenient; they don't want to stay home to wait for a repair person,'' the Whirlpool spokeswoman says. As more easily replaceable modular electronic components are used, she predicts, customers will do most of their own servicing.

If appliances have been a buyer's market, is it too late for investors to buy stock in these companies? Probably, many analysts say.

''Just as housing has topped out,'' says Mr. Magid at L.F. Rothschild, it looks as if appliance sales have topped out. ''GE has already had some layoffs.''

Mr. Ryan's industry outlook for the last quarter of 1984: ''We expect sales will be up less than 5 percent on a year-to-year basis.'' (Through September, total sales were up 24 percent over 1983.)

Meanwhile, microwave oven sales will grow 10 percent next year, predicts Ryan. This bodes well for Magic Chef, which this year picked up market share with brisk sales of microwave ovens and Admiral refrigerators (featuring an ice cream maker).

Next year, the Merrill Lynch analyst expects a slower-growing economy will mean total shipments will rise or fall about 3 percent. ''I don't think appliance stocks will become attractive again until well into 1985.''