The late Walt Disney's last and greatest dream is scheduled to become reality in October, 1982. When it does, it could very well put the business of World's Fairs -- as we know them today -- out of business.

Before he died almost 15 years ago, Disney -- whose pioneering efforts in cinema animation revolutionized the entertainment industry and whose visions of theme parks changed the travel habits of millions of vacationers -- envisioned a permanent, futuristic exposition with international overtones. The project would be called EPCOT, or Experimental Prototype Community of Tomorrow.

The stuff Disney's dreams were made of is rapidly taking shape here on Disney World property a scant two miles south of the Magic Kingdom, another of the showman's dreams and probably the most successful entertainment destination the world has ever known.

The EPCOT site covers 600 acres, 200 of which will contain the permanent pavilions. The 400 additional acres have been set aside for parking lots, landscaping and future expansion. The $800 million project is the largest ever undertaken by the Disney organization. [The original cost of Disney World on opening day, Oct. 1, 1971, was $400 million, including land, utilities, attractions. Disney officials hope that the entire cost of EPCOT will have been returned by opening day 1982, through the amusement park's profits and participation agreements with countries and corporations.]

EPCOT will have two principal themes: Future World, and the World Showcase. Many of America's corporate heavyweights -- AT&T, Exxon, General Motors, Kodak, Kraft, General Electric -- have already made commitments for pavilions at the Future World project. The World Showcase theme has garnered nine countries: Canada, the United Kingdom, France, Germany, Italy, Israel, Japan, Morocco and Mexico.

The United States isn't sponsoring a pavilion, but Coca-Cola and American Express have teamed up to offer The American Adventure, which will tell the story of our country's heritage in a show they say "will be unparalleled in Disney annals."

Mind you, a commitment to EPCOT is no small potatoes. Any country or corporation has to sign a 10-year contract to be part of Disney's greatest dream. Although none would say how much they were anteing up, the figure most commonly heard is in the tens of millions of dollars.

Those going into the initial phase of EPCOT feel it's more than a safe bet and that the investment is well worth it. Unlike World's Fairs, it is a longrange project. World's Fairs traditionally run in the red because they require major investments and are only temporary -- running for about six months. The Disney project is to be a permanent showcase, a Disney spokesman said -- "the only international exposition of its kind anywhere."

So sure are they of EPCOT's success that Disney World already has planned for new pavilions to open in 1983. One of them, The Seas, will feature the world's largest salt water aquarium, with 5.7 million gallons of water.

In addition, new hotels are being planned for the area, while others are being expanded. Eastern Airlines, the "Official Airline" of Disney World, already is drawing up travel packages including the new facility, which will be linked to the Magic Kingdom by monorail. At the same time, Orlando International Airport is undergoing a $231 million facelift to be completed by the end of 1981 -- in plenty of time for the EPCOT opening.

With EPCOT's opening, 20 million visitors a year are expected to tour the Disney facilities and the figure is expected to zoom from there. Right now the Magic Kingdom plays host to 14 million visitors annually. Currently, visitors stay in the area for an average of three days, but with EPCOT their length of stay is expected to be at least five days.

An admission price for EPCOT hasn't been decided upon. A Disney World spokesman said it would be about the same as the Magic Kingdom, where a one-day adult admission, including transportation by monorail or ferryboat and entrance to 10 attractions, now costs $11.50 -- $10.50 for juniors 12-17 and $9.50 for children 3-11. (This new ticket book is in addition to a Two-Day Passport offering unlimited use of attractions except for the shooting gallery.)

Even with the big push toward the future with EPCOT, the present is alive and well and living happily in the Magic Kingdom. A new attraction -- Big Thunder Mountain Railroad -- recently opened and is booming success. Though Disney officials have not put a price tag on Big Thunder, they have indicated that it cost more than the $17 million spent to open Disneyworld in Los Angeles in 1955.