Take a tour by streetcar. That's the latest tip for visitors to New Orleans. And to put the idea across, the city has inaugurated a $4 all-day pass on the St. Charles Avenue electric line through the Uptown District.

The pass, along with an unusual booklet called "Streetcar Guide to Uptown New Orleans" is aimed at introducing tourists to a part of the city they often fail to see. The pass went into effect last month.

The St. Charles line has been around a long time. In fact, it began back in 1835 and is the "oldest continuously operated street railway in the world." A few years ago it gained a spot in the National Register of Historic Places. But the emphasis for New Orleans visitors always has been on the popular French Quarter, with its jazz spots, shops, restaurants and other entertainment.

The streetcar ride along St. Charles Avenue covers a century and a half of architectural styles. It cuts across the modern business district, past Lafayette Square and Lee Circle with their statues, through the Garden District with its historic old mansions in beautiful surroundings, past Tulane and Loyola Universities to spacious Audubon Park.

The 350-acre park, once a plantation, extends from St. Charles Avenue to the Mississippi River and contains the city zoo, a golf course, tennis courts, swimming pool, bridle paths and even a miniature train. Great oaks oaks shade paths for strolling.

The present streetcars, built in 1923-24, have old-fashioned wooden seats that can be reversed, depending upon the car's direction. The seats also have brass hand grips on the aisles for standees. Recently, exact fare boxes were installed, allowing for a one-man operation.

The streetcars clang along the 6.5-mile stretch with frequent stops and the journey one way takes about 45 minutes. A round trip gives you an overall view of the sights, and then you can return for a closer look at what interests you the most. That's where the $4 pass comes in handy. The cars run about every seven minutes, and you can get off all day long anywhere along the route. Without the pass the fare is 40 cents (exact change) every time you board the car.

"The Streetcar Guide to Uptown Orleans," a 136-page paperback, outlines self-guided walking tours at various stops, gives the background of the old homes and buildings, and carries a directory of shops and restaurants. Actually, it tells the history of New Orleans since its founding back in 1718.

Newly-numbered car stops, coordinated with maps in the guidebook, provide the streetcar traveler with easy-to-follow exploratory walks in the neighborhoods adjoining St. Charles Avenue, as well as along the street itself. Peak local traffic on the cars headed uptown is from 4 to 6 p.m. on weekdays and it's advisable to avoid those hours if possible.

The streetcar guide is available for $5 throughout New Orleans at bookstores, hotels, motels and gift shops. It also can be bought at the Streetcar Store on St. Charles near the first car stop. It's in this store, too, that you can purchase the $4 pass.

If you want to study what Uptown New Orleans has to offer before you go, the guidebook can be purchased by writing the Streetcar Car, 111 St. Charles Ave., New Orleans, La. 70130. The price by mail is $5.75.