For Kaydeross Park, the final days of the summer of '87 mark the end of the squeal and clatter of fun. The 40-acre amusement park, perched on the edge of the lake, has been sold to make way for 349 units of luxury housing called The Vista. Its last day of operation is expected to be Sept. 20, three days before the official end of summer.

Already, signs of "progress" abound: a trim real estate office now overlooks the park, and a section of the grassy parking lot has been sliced open by bulldozers and divided by orange surveyor's tape into future plots.

On Oct. 2 and 3, the Michigan-based Norton Auctioneers will sell off all the rides and games that have spun and twirled for the past three decades: the Wild Mouse roller coaster, the Tilt- a-Whirl, the Paratrooper, the Caterpillar, the bumper cars and boats.

"We've had people call interested in some of the things," said state Assemblyman Robert D'Andrea, R-Saratoga Springs, one of the owners of the park. "One guy wanted to buy all the rides."

THIS IS, of course, merely a sign of the times. Amusement parks are not what they used to be, said John Graff, director of the Virgina-based International Association of Amusement Parks and Attractions.

The parks first appeared in the United States at the end of the 19th century, when railroad companies would build them outside cities to increase ridership on the weekends, Graff said.

In the 1920s, when amusement parks were at their "peak point," there were nearly 1,000 of them across the nation, Graff said. Today, Graff's group consists of 450 parks, which, he said, is nearly all the parks in the United States.

The number of parks dwindled during the Depression and after World War II with the exodus of people from the cities to the suburbs. The trend continues today.

Between 1982 and 1987, 26 parks closed nationwide, including one each in New York City and Canandaigua, according to the Amusement Parks Guidebook for 1987. Five more have "uncertain futures," while three dropped below eight rides, according to the guidebook.

"Pennsylvania probably has more than any single state," Graff said. "Then New Jersey, New York, Ohio, Florida and, of course, California. Those would be the big states."

In recent years, the parks - usually located on valuable land near a city - have fallen victim to real estate frenzy: developers have been buying them up to build housing developments. This is what has happened at Saratoga Lake.

THE KAYDEROSS Park owners - Walter and Jerry Wrobel, and D'Andrea - got tired of running the park after 31 years of ownership. Though attendance was increasing, D'Andrea said, the owners decided to sell out.

Along came developer Robert Kohn with a plan to build 349 single-family and town-house units that would cost more than $200,000 per unit. In April, the project got the approval of the Saratoga Springs City Council.

The closing of Kaydeross and of Brown's Beach, two private facilities both open to the public, will leave the state boat launch as the only public access to the lake.

On a recent day at the park, a few of those in attendance at Kaydeross recalled the past with affection and the future with apprehension. It was a typical day, the jingle of children's voices and the rock 'n' roll music of the merry-go- round filling the air.

"It's condominiums or some idiotic thing," sighed Helen Donnelly of Boght Corners in Colonie, who was visiting the park with her grandchildren and her sister, Eleanor Donahue of Greenwich.

Neither had visited the park in a long while, and while sitting under a yellow-and-white- striped umbrella as children ran to and fro, they agreed that looking back was a lot more comforting than looking forward.

"It's a shame," Donahue said.

"It's all over," Donnelly declared. "All the farmland's going. They're putting in three-lane highways and things like that."

Ed Mahan, a Hudson Falls corporate controller, had visited the park for the past three years. With his son, Tommy, "almost 2," in a stroller, Mahan talked of the planned luxury housing as he would a plague of locusts.

"This whole condo idea" revolted him, Mahan said, as teenage girls nearby attempted to dethrone straw dolls with plastic baseballs. "All in the name of progress. If that's progress, they can have it."

AMUSEMENT PARKS do have a future, though they won't look like Kaydeross. The new-wave Super Mall Amusement Park that first appeared in Edmonton, Canada, two years ago now is spreading across the United States.

"This isn't some mall putting up a Ferris wheel in the parking lot," Graff said. "This is a full-blown amusement park inside a mall."