Besides four wheels, a backseat driver and saddle bags full of silver to pay for full, the highwayman in these days of cloverleafs, throughways, roundabouts and shunpikes needs a navigator. Any reasonably intelligent person with a degree in highway engineering and a postgraduate course at the Cornell hotel school will do.

In Europe, the art of navigating has been reduced to a simple science by the Michelin people, who are tire merchants by trade but publish a vast library of maps, red guides and green guides. The red guides tell where to stay and eat, as well as how to get there. The green guides, not available in English in all areas, tell what to see.

TFor those touring along the master network of roads in the United States - and that amounts to more than 100 million people aa year - the handiest piece of equipment aside from a jack and a spare tire is a Mobul travel guide. Available in seven volumes, each contains places to see, places to stay and noteworthy nests of nourishment.

Like Michelin is grades restaurants and awards stars. Three stars is the top grade awarded by the tire people, but in America the gas people go up to five. By Michelin standards there are 18 three-star restaurants in France, but there are only nine five-star restaurants in the whole United States, if you take the word of the old folks.

Those who are fascinated by such incidential intelligence can mull the list: Ernie's in San Francisco, Rancho Del Rio Tack Room in Tucson, Le Perroquet in Chicago, Cafe Chauveron in Miami, Petite Marmite in Palm Beach, Tony's in St. Louis and Le Ruth's in New Orleans.

New York's "21" Club didn't make it. Neither did La Caravelle, which the resident French vote as perhaps the best French restaurant this side of Le Taillevent (Paris). Mobil never heard of ReRgine's, whose cuisine is supervised by Michel Guerard (whose place in the Pyrenees won three stars). Le Bistro in Los Angeles didn't get a look. Neither did Bookbinder's in Philadelphia or Locke Ober in Boston.

Just how do these geologists of gastronomy strike oil where they do?

The guidebook editors maintain a corps of field representatives, mostly mature, retired people. Many are professors put to pasture and at least one is a retired admiral.

Inspectors are likely to be people who have traveled, and who will not be impressed by the first fancy place they enter. They are trained and given a set of forms to fill out - one form for hotels, another for motels, a third for resorts and a fourth for restaurants.

Although Michelin's writers who prepare the green sightseeing guides will grade places according to their worthiness, Mobil makes do with a list of things to see provided by state tourist bureaus and local chambers of commerce. Opening hours and admission costs are sights are listed implies no preference. No inspection is involveed in sights listed by Mobil, so in that category the traveler takes his chances.

When it comes to lodging, the inspector snoops about the grounds, looks at the public rooms as diffidently (but as discerningly) as possible,, and then identifies himself. He requests to see one room in each category from suite to what is called a single. A single is one bed in one low-cost room, usually over the parking lot.

The inspector doesn't stay in the lodging and thus doesn't have an opportunity to test the service. He makes a recommendation on his form, and that, together with cards that come in from readers, determines the rating. Twenty-one places of lodging rate five stars, among them Stanford Court in San Francisco, Washington's Madison Hotel, the Arizona Biltmore and the Greenbriar in West Virgins.

Four resorts out of nine that got five stars are in Arizona. The only two motels that made it are both in Oregon. And two of the three hotels in New York that are knighted are mostly filled by permanent guests who occupy apartments.

When it comes to restaurants, Michelin would scarcely award Mobil one shrug - let alone one star. A Mobil inspector can order a meal but he doesn't have to. He inspects the kitchen, looking for cleanliness and size. For this he has to make himself known. Everything after that is assessed after he has blown his cover.

He looks to see if the meat is separated from the fish in the storage areas. He examines the size and quality of the wine cellar, but he doesn't taste. Mobil counts on its mail for reaction from the customers. It gets 50,000 pieces a year, each a pat or a pan. Those who write are really concerned with the better places and therefore listings in the potential multi-star red categories get special attention.

A limiited wine list once cost a famed Boston seafood restaurant a five-star listing, very nearly setting off a new Boston tea party. In Florida a well-known resort went down two years in a row. Based on reports from readers of the guide, the manager sent in some undercover "guests." They found the maitre d'hotel was selling poolside tabless and the bartendeer engageed in some private ripoffs of his own.