THE BEST FASHION show in Paris is on the streets. That's fortunate, since it is almost impossible to get in to see the major French designer shows that attract thousands of buyers and the press several times a year. In fact, many of fashion's officialdom -- even the store executives who travel to such world fashion centers as Paris and Milan -- must share the limited seats available for the runaway shows.

But that doesn't keep them from going to Paris, because there is much to learn from the way the French dress on the streets, in boutiques, restaurants, tea rooms, discos and the theater. And from the displays in boutiques, the fashion-conscious get a worthy view of upcoming trends plus innovative ways of display and decoration.

Nevertheless, fashion presentations are available. The houses of Christian Dior and Chanel put on low-key shows for the public twice weekly, usually weekday afternoons. Pierre Cardin accepts group admissions only, charging a fee that, it says, is tailored to the size of the group (no hints offered). A few other houses invite outsiders to see audio-visual presentations of their designs.

"Les Coulisse's de la Mode," a commercial presentation with both audio-visual and live models, has been temporarily discontinued. However, it would be worth checking with that organization before your trip to see if these shows have been revived. (The most recent price quoted is $24 for a two-hour show with cocktail; $40 for the show with lunch.)

To insure your best chances for seeing a Paris fashion show:

* Write in advance: A dignified note on engraved stationery or formal business stationery and the mention of a swanky Paris hotel as your place of sojourn will boost your chances.

* Check with the concierge of your hotel: Theoretically, the concierge will be current on which houses permit tourists to their showings. No surprise, the fancier hotels (and their concierges) have the most success in getting their guests into shows.

* Call the fashion houses directly: The telephone book with listings by professions has fashion houses listed under "couture," "couture cre'ation" and "couture (haute)." Learn to pronounce the name of the designer before you dial the number--no one appreciates having his or her name mispronounced, particularly French designers and their coterie. Polish up your best French grammar and most formal idioms--they count with the French--and ask for the attache' de presse (the press office deals with all public matters). Sound official, dignified and rich.

Whether or not you get into a fashion show, just being conscious of the people around you, even on the me'tro or walking through a museum, will give you lots of ideas about clothes--not only what's new, but more stylish ways to wear what you already have, fresh color combinations, new hairstyles, makeup trends and the like.

Paris fashion watching is at it's best at:

* La Coupole (102 Boulevard Montparnasse, 75014): A favorite hangout of the fashion and literary crowd who usually arrive after 11 p.m.

* Le Relais Plaza Grill (31 Avenue Montaigne, 75008): The superdeluxe coffee shop in the Hotel Plaza Athene'e (10 asparagus in season for $18 at last count). Emanual Ungaro, whose boutique is across the street, occasionally lunches here, and so do the French and the tourist crowds. (If you can't afford the lunch tab, check out the lobby. The crowd mix is likely to include one Hollywood celebrity, 12 rich Texans, two French royalty and 16 Arabs.)

* Cafe' des Deux Magot and Cafe' de Flore (just off Place St.-Germain des Pres): Bundle up and sit outside to watch the passing show of young Parisians on the left bank. Saturday afternoon is the best show.

Brasserie Lipp (151 Boulevard Saint Germain, 75006): Good international mix of the professional fashion world and a clientele that is well dressed.

Carette (4 Place du Trocadero, 75016): Tea room in the Trocadero famous for chocolate macaroons and a well-dressed crowd.

Angelina (the old Maison Ruplemayer, 226 rue de Rivoli, 75001): A famous tea room, to which the lovely, elegant older women of Paris come daily--and so do some young women.

Any Japanese restaurant: The current fad in Paris, a favorite of the young because the food is fresh, attractively presented and you can eat lunch rather speedily if you want.

Le Palace (8 rue du Faubourg Montmartre, 75009): Hangout of the fashion groupies and crazies. Seeing is believing. It is also a pet place of designer Karl Lagerfeld and Paloma Picasso and their chums. They usually dine downstairs in Le Privilege, but they walk through the long entranceway to get there. Leave at home your pearls and button-down shirts. When in doubt, wear a black sweater.

The ultimate fashion gathering is the showings in Paris in mid-March and mid-October. The fact that you can't get into the actual shows should not curb your effort to see the scene. The entire fashion world--models, designers, retailers, editors, photographers and hangers-on from Japan to Georgetown--crowd around the tents for the twice-yearly, week-long marathon of fashion shows. It is worth the frenzy and the fuss.

You have nothing to lose but complaceny about your own wardrobe.