Recent market research suggests that fat-free and reduced-fat foods are not doing as well as they have in the past. More than ever, taste is the No. 1 consideration when people buy food.

And mayonnaise, without which a tuna sandwich and a potato salad can hardly be made, is showing some signs of this trend. According to Best Foods, the manufacturer of Hellmann's Mayonnaise, low-fat and no-fat mayonnaises from all companies accounted for 28 percent of the market in 1989; today they account for 20 percent. (Hellmann's is sold in the western United States under the Best Foods label.)Mayonnaise is the suspension of oil in egg yolks. Nothing more; everything else is flavoring. But that basic prescription went out the window when mayonnaises were invented that were non-, low- or reduced-fat, not made with eggs at all or made with tofu.

Most of the lower-fat alternatives cannot compete with full-fat mayonnaise in a taste test, and certainly none are as good as mayonnaise made at home, the best of which will include some olive oil. Homemade mayonnaise does not call for sugar, but most commercial brands contain some form of sweetening.

Is it possible for people who monitor their intake of fat and calories to find a good-tasting, lower-fat mayonnaise? To find out, I bought 13 low-fat mayonnaises and salad dressings. Fat-free versions were not even considered for this taste test because my experience with fat-free mayonnaise and almost anything else fat-free has not been pleasant.

The mayonnaise against which all these brands were compared was Hellmann's Real Mayonnaise, because of its consistent ranking as the best seller. Hellmann's Real Mayonnaise has 100 calories and 11 grams of fat a tablespoon. (Out of curiosity, I also tried Walnut Acres All Natural mayonnaise, which contains 17 grams of fat, just to see if it tasted better than Hellmann's. It did.)

Usually, but not always, the greater the amount of fat and calories in a mayonnaise, the better the taste. But in my test there were several pleasant surprises.

Hellmann's Light, with 50 calories and 5 grams of fat, was quite acceptable , and Bright Day Dressing, made without a single egg yolk and containing only 60 calories and 6 grams of fat, made up for its lack of fat with a good dose of vinegar and mustard that gave it a decent flavor.

Some flaws that are obvious in lower-fat mayonnaises when they are tasted "straight" largely disappear when they are mixed with other ingredients that often go into salads like lemon juice, mustard, pickle relish or capers, or if they are mixed with flavorful herbs like thyme, basil, dill or tarragon.

A simple way to reduce the fat and calories in full-fat mayonnaise without seriously disturbing the taste is to mix half mayonnaise and half plain low-fat yogurt. Only the most flavorful mayonnaises are suitable for this adjustment.

In flavor, the best of the 13 was the Ojai Cook Lemonaise with 90 calories and 9 grams of fat. That is not much of a reduction from full-fat Hellmann's, but because of its sharp flavor from lemon juice, Dijon mustard, cayenne pepper and garlic, this tangy alternative is just delicious. But the price difference is huge: an 8-ounce of jar of Hellmann's s $1.35 while a 10-ounce jar of Lemonaise is around $5. And worth every penny.

In search of an alternative to full-fat, high-calorie mayonnaise, I sampled 13 varieties that had fewer calories and fat than the benchmark brand, Hellmann's Real Mayonnaise, which has 100 calories and 11 grams of fat a tablespoon.

The latter has a creamy, pleasant, slightly sharp taste. Among all mayonnaises, it is consistently the best seller.

The best-tasting mayonnaises, those ranked in the first tier, ranged from delicious to accep-table.

In the second tier, they were acceptable only when mixed with the tuna and seasonings.

In the third tier, all had unappealing flavors.

FIRST TIER

The Oaji Cook Lemonaise , 90 calories, 9 grams fat a per tablespoon. Tangy, gutsy, flecked with whole-grain mustard seeds; only real ingredients used; 10 ounces, $4.99.

Hellmann's Light Mayonnaise , 50 calories, 5 grams fat. Good texture, slightly less tart than Hellmann's Real Mayonnaise; 32 ounces, $3.59.

Bright Day Dressing , 60 calories, 6 grams fat. Stiffer texture, pleasant very tart-sweet taste; 16 ounces, $2.99.

Vegenaise Dressing and Sandwich Spread , 90 calories, 9 grams fat. No eggs. ; sharpest taste is from vinegar; 16 ounces, $3.69.

SECOND TIER

The New Weight Watcher's Light Mayonnaise , 25 calories, 2 grams fat. Good texture, tart, slight chemical aftertaste; 32 ounces, $3.29.

Hellmann's Low Fat Mayonnaise , 25 calories, 1 gram fat. Fairly bland. ; 16 ounces, $2.45.

Kraft Mayonnaise Light , 50 calories 5 grams fat. Quite bland, leaves an oily film on the roof of mouth; 32 ounces, $3.19.

Cain Reduced Fat Mayonnaise Dressing , 25 calories, 2 grams fat. No taste. ; 32 ounces, $2.99.

Kraft Miracle Whip Light Dressing , 35 calories, 3 grams fat. Sweet and floury; 32 ounces, $3.89.

THIRD TIER

Nayonnaise Vegi Dressing and Spread , 35 calories, 3 grams fat. Tastes only of tofu; 14 ounces, $3.19.

Salute Sante , 90 calories, 9 grams fat. Predominant flavor is grape-seed oil; 17 ounces, $7.95.

Spectrum Lite Canola Mayonnaise , 35 calories, 3 grams fat. No eggs, pasty texture, vinegary taste. ; 16 ounces, $3.29.

Walnut Acres No Yolk Mayonnaise , 80 calories, 9 grams fat. Doesn't taste like mayonnaise; 16 ounces, $4.69.