This time of the year, the marquees at many drive-ins say ''closed for the season.'' But with 13 percent of the outdoor theaters having shut down in the last decade, a more common feature is just plain ''closed.''
Oddly, however, the decline of this industry is making owners rich, not poor.
''Most drive-ins, like most public golf courses, are not created to be revenue earners, but to maintain property cheaply while the land increases in value,'' says Mark Manson, an analyst at Donaldson, Lufkin & Jenrette, an investment house. ''Originally, the drive-ins' proliferation was not so much related to their popularity as to the rising value of real estate.''
And as cities have lapped out farther into cow pastures, property values there have risen with the tide. For example, the 14 acres which the Morris Plains Drive-In in New Jersey occupied, valued at $10,750 in 1947, was sold for a reported $1.25 million last year.
''In general, drive-ins aren't operated at their most valuable and productive use,'' says Fred Wineland, president of Wineland Enterprises, which runs four drive-ins and one indoor theater outside Washington. ''So you sit on them until you can sell them, rent them, or build them up yourself.''
Property taxes - also an indication of the increase in land values - have bloated ''until it's almost unbelievable,'' thereby putting cost pressures on drive-ins, Mr. Wineland complains. He estimates the property taxes on his drive-ins have increased between 600 and 1,000 percent in the last 20 years.
In recent years, profits from drive-ins have been squeezed practically dry. Aside from rising property taxes, increased film rental costs have hurt drive-ins more than indoor theaters. Instead of making 30 low-cost, low-rental films, the movie industry is turning out fewer, very expensive films like ''E.T. ,'' says Mr. Manson at Donaldson. So theaters need more revenue per film to cover rental costs, which can be as high as 90 percent of gross profits for popular films. As a film plays longer, the percentage going to rental fees declines. Thus, theaters must play movies longer to make it worth their while.
But ''drive-in moviegoers want a new feature every week,'' says Scott Cohen, vice-president of R.C. Theaters in Baltimore. ''And (movie studios) don't make the kind of movies that were the bread and butter of drive-in business: the black exploitation films, karate films, and racing pictures. That's what drive-in customers want to see.''
In 1974, R. C. Theaters ran 20 drive-ins; now it owns 9, ''and we're getting rid of them as we can,'' Mr. Cohen says.
Filmmakers are bypassing drive-ins for use on cable television and home video. Because of rental costs, drive-ins generally play second-run films - which eventually appear on regular TV, or immediately on cable TV. With drive-in movie attendance dwindling, filmmakers can reach a larger audience and make heftier profits with home-video.
Drive-ins, furthermore, are cultural dinosaurs. ''The car is not a part of American culture as it used to be,'' Mr. Manson said. ''The classic image is (of a family) going to a drive-in in a Pontiac, not a Toyota.''
Finally, the appeal of a drive-in - being outdoors - is also its undoing. Eastern daylight time thwarts theater owners in the summer, pushing film times past an hour when many families want to take their children out. In the North, most outdoor theaters are only open two to four months a year. Only in the Sunbelt states are drive-ins holding their own.
In a last-ditch effort to keep their drive-in a drive-in, some owners, mainly in the South, are setting up ''multiplex'' screens - with several screens playing different movies on the same field. Multiplexing is made possible by radio sound, in which the sound is transmitted in the area of the drive-in. A viewer tunes the car radio to a place on the dial not occupied by a local station to hear. ''After you make the initial investment for new screens, most people find it's cost effective,'' says Jerome Gordon of the National Association of Theater Owners. ''You increase your attendance and keep the same staff, so you have lower costs per showing and per customer.''
Another, more lucrative, option is to convert outdoor theaters into indoor theaters. For example, the Redstone Theater's Long Island drive-in was doing fine a couple of years ago, says Samuel Feldman, vice-president of the fifth-largest theater chain in the country. The drive-in could hold 1,800 cars, or about 6,000 people, and attendance was pretty good.
''But no drive-in is filled, and the business is expected to drop off even more,'' Mr. Feldman said.
So Redstone built an 11-screen indoor theater complex - which still holds 6, 000 people. On weekends, it is entirely filled. Sunrise Multiplex is now the busiest theater in the US, he says, and because each film can be shown several times, it has eight times the volume.
Finally, drive-ins can be sold for cash, most frequently to developers building shopping centers and office parks. Most drive-in owners, like Fred Wineland, are not particularly wedded to their plots of land. While his drive-ins are currently profitable enough that he wants to retain them, Mr. Wineland muses, ''If somebody comes along and makes me an offer I can't refuse, well, a business decision is a business decision.''
All this spells the end of a cultural era. As John Zawalich of Redstone Theaters observes, ''Drive-ins are slowly but surely biting the dust.'' But not the theater owners, who profit nicely when the marquee reads ''For sale.''