The Griffith Observatory, the backdrop for dozens of movies, a favored make-out spot for generations of teenagers and, not to be overlooked, a substantial educational and scientific institution, will reopen this fall after a four-year foundation-to-dome renovation.

While many visitors take the winding drive through Griffith Park to the observatory chiefly for the panorama of the vast city from the promontory where it sits, the observatory also serves as a gateway to the cosmos for at least some of its two million annual visitors.

When it reopens, it will have one of the world's most advanced planetariums and dozens of new astronomy exhibits, as well as the 12-inch telescope and an instrument for tracking the sun that were installed when the observatory first opened in 1935.

The concrete, brass and copper exterior, an amalgam of Art Deco, Beaux-Arts, Greek and Egyptian themes, has been restored to the original 1930's design of Russell W. Porter, an architect and amateur astronomer.

Except for the Hollywood sign just to its west, the observatory is perhaps the city's most recognizable landmark, visible for miles.

Edwin C. Krupp, the scientific director of the observatory since 1974, said the Griffith was the most-visited public observatory in the world, designed to turn the tourists who wandered up to take in the view of the city into observers of the universe.

''It is a familiar icon of Los Angeles,'' Dr. Krupp said as he led a tour of the unfinished exhibit spaces this week. ''It is, in fact, the hood ornament of Los Angeles.''

The 4,100-acre Griffith Park, one of the largest urban parks in the nation, was a bequest of Col. Griffith J. Griffith, an eccentric early Los Angeles land buccaneer who was struck by a pang of public-spiritedness before his death in 1919. He financed the construction of the observatory and the nearby Greek Theater and left enough money to assure that admission to the observatory would always be free.

The observatory originally cost $400,000 to build and equip. The renovation will cost $93 million, including $67 million in public money. While the exterior looks basically the same as the original, nearly 40,000 square feet of exhibit and office space has been added by excavating under the front lawn and the west terrace.

The new exhibits include a highly detailed composite photograph of a slice of space that is 150 feet wide and 20 feet high. A million galaxies and a half-million stars are visible in the photograph.

The heart of the observatory remains the 300-seat planetarium, newly equipped with a $7 million Zeiss Mark IX Universarium, the world's most advanced star projector.

But the Griffith is probably better known for its role in films than for its educational mission. The observatory has appeared in scores of movies, including Arnold Schwarzenegger's original ''Terminator'' and Disney's ''Rocketeer,'' as well as a 1995 episode of ''Star Trek: Voyager.'' Just west of the observatory is a bust of James Dean, noting the building's co-starring role in the knife-fight scene in ''Rebel Without a Cause.''

''We've been in so many movies we ought to have a star on Hollywood Boulevard,'' Dr. Krupp said.

Before the observatory shut down in early 2002 for the renovation, Dr. Krupp recalled, he asked visitors what they would miss most about the place. The view, they answered.

In Southern California, it is said, topography is destiny. The observatory sits on Mount Hollywood, a few miles north and west of downtown Los Angeles. Twenty miles to its west, on a hillside in the Santa Monica Mountains, sits the other popular cultural bookend of Los Angeles, the Getty Center in Brentwood. It, too, is the bequest of a wealthy refugee from somewhere else, J. Paul Getty, and it, too, is visited as much for its views and public spaces as for its artistic collections.

''Height has always meant authority in Los Angeles,'' said D. J. Waldie, a longtime city official in the suburb of Lakewood, and the author of several books about Los Angeles. ''In Southern California, our gods are all gods of high places.''

He said Colonel Griffith, Mr. Getty and others who had made their names and their fortunes here staked out the city with monuments to make it more than a wide spot on the road to somewhere else. ''We can be skeptical about the quality of the monuments and the art inside,'' Mr. Waldie said, ''but a place is made by literally putting down a foundation in the ground. These buildings are at least partially successful efforts to make what sometimes seems a flimsy and ephemeral place seem less so.''

Photos: A telescope at the Griffith Observatory, which is completing a $93 million renovation.; The Griffith's memorial to James Dean. (Photo by Monica Almeida/The New York Times); From atop Mount Hollywood, the Griffith Observatory will again offer breathtaking views of Los Angeles and the universe. (Photographs by J. Emilio Flores for The New York Times)