Apropos of the ''undercover'' world, there's an amusing anecdote about Greta Garbo that's making the rounds. The legendary star once insisted that the studio provide her with innumerable sets of pure silk lingerie to wear beneath the film wardrobe, although nary a glimpse of the underpinnings would ever be seen on the screen. The producer complained vociferously over the cost, claiming that inexpensive rayon underwear would do just as well and no one would ever know. ''But I will know,'' said Miss Garbo, ''and it will make all the difference in my performance.''
Few people can afford the luxury of pure silk today, and even fewer care to cope with the upkeep. Gone are the days when French ladies' maids painstakingly pressed hand-sewn pleats and embroidery. When it's a do-it-yourself deal, that bias-cut silk satin nightgown or slip seems to slither around beneath the iron (yes, silk has to be ironed and constantly treated with tender, loving care) and usually ends up sagging longer at one side or cowling in front like a kangaroo's pouch.
Yet there are still a few ultra-luxurious lingerie shops in Paris, plus couture boutiques. A prospective bride will often splurge on one glorious ensemble: a peignoir and matching nightie or a superb negligee cut with all the simplicity of a man's dressing gown or kimono. Most of us settle for polyester and synthetic satins, knowing we don't have to wear them for years to amortize the investment.
If the majority of the fabrics are totally modern, many of the current styles are slightly retro. Back comes the ''teddy'' from the 1930s, that charming little one-piece undergarment with camisole-style top that doubles as a modesty piece beneath a decollete or sheer blouse.
Lingerie appears in effective coordinates for both daywear and nighttime. Black, white, and ivory (in that order) are the leaders, according to statistics from the French lingerie syndicate. Yet many women prefer pastels: peach, mango, lavender, and marron glace. Long shots this winter will be navy and tomato red.
Bedtime, and the story is still as pretty. Give those dormitory pajamas inspired by jogging gear right back to the joggers and opt for anything feminine , from the long-sleeved, high-necked, and ruffled nighties reminiscent of a Victorian trousseau to the prewar Hollywood glamour immortalized by Rita Hayworth and Lana Turner.