Wayne Bachand and his family fulfill Disney World's greatest fantasies and its competitors' greatest fears. The Bachands visited Florida for six days; they remained at Disney World for six days. They leave happy and satisfied.

"Why should I go anywhere else?" says Bachand, of Manchester, N.H. "This place has everything I want."A pioneer when it opened 17 years ago, Disney World already dominates Florida tourism. Now, a third major playground - Disney-MGM Studios Theme Park - officially opens Monday at Disney World, and the company has other ambitious attractions and at least four more hotels on the way.

Disney is tightening its grip, and competitors are feeling cramped. Some say Mickey Mouse is turning into a selfish rat.

"Disney would like to capture as many of the tourists' days as it can," says Janeen Dunbar of Wet 'n Wild, a water theme park in Disney World's shadow. "We know we've got to keep an eye on them."

Disney executives, huddled over their expansion plans and smiling like Cheshire cats, make no apologies.

Forget Bambi and Tinker Bell. This is a business, and these are the guys who sue the Academy Awards for alleged misuse of Snow White, the guys who send investigators to out to bust day-care nurseries for unauthorized use of Donald Duck and Jiminy Cricket murals.

Disney executives once spoke as though they were pleased to share the bounty with other attractions. Now, they've changed their tune.

"We want to build on the tourist base we've developed over the last 17 years," says Tom Elrod, Disney World's senior vice president for marketing. "To capitalize on what we've built ourselves is not selfish."

There is more bad news for competitors: An international consortium wants to build a bullet train to speed tourists from Orlando International Airport to Disney World in less than seven minutes, affording them hardly a glimpse of other attractions.

"Disney might just as well build its own airport and buy its own airline," says Tim O'Brien, managing editor of Amusement Business, an industry newsletter. "That's what it's coming to."

No one is thinking about boarding up and moving away, but most of Disney's competitors are wondering how they can remain fat and happy on a reduced diet of Disney leftovers.

With its third theme park ready to go, Disney World is scrapping its $78 three-day "Passport" and replacing it with a $97 four-day and $112 five-day pass.

So Disney's plan becomes clear: Don't leave tourists with much time or money to go elsewhere.

"It's a good business strategy," says Walter Klages, president of Research Data Services Inc. of Tampa, a tourism consulting firm. "No one can accuse them of a criminal activity. It's just good strategy."

Analysts say Disney is certain to tighten its grasp in coming years. Nearly all of its new attractions compete head-on with existing or planned attractions in the area.

And Disney has one overwhelming advantage.

"Most of the people are already on their property," says Abraham Pizam, a tourism expert at the University of Central Florida.

On Monday, the company opens its Disney-MGM Studios Theme Park, a $400-million, 135-acre celebration of movies and television. The mammoth park features adventure rides, backstage exhibits, audience-participation shows and tours of Disney production facilities.

It will compete directly with Universal Studios Florida, a tourist attraction only 12 miles away that was announced several years ago but is not scheduled to open until next year.

This competition does not please Universal executives. Sidney Sheinberg, president of Universal's parent company, recently asked the Orlando Sentinel, "Do you really want a little mouse to become a large ravenous rat?"

This summer, Disney plans to open Typhoon Lagoon, a water-sports theme park that will compete against Wet 'n Wild.

It also will open Pleasure Island, six "themed" night clubs that target conventioneers who now visit Church Street Station, an entertainment complex in downtown Orlando, and teenagers who now visit Boardwalk and Baseball, a theme park just down the road from Disney World.

Also on line at Disney World are at least four new hotels, including the state's largest - 1,510 rooms - in what Disney officials are calling the Conventional Kingdom. By the mid-1990s, Disney is expected to have 15,000 hotel rooms, more than one-fifth of all the rooms in Central Florida.

Once bivouacked in Disney hotels, most of which are self-contained resorts designed to refresh theme park weary visitors, tourists are essentially captured. Even Domino's Pizza won't deliver to Disney hotels.

"Disney has decided to go into the hotel business full steam ahead," Pizam says. "They realized they already have the bodies in their parks, so why not have the bodies sleep in their properties?"

Backing all of this are 17 years of extraordinary success, a reputation as a clean and safe vacation center for children and adults - Disney World already is the world's leading honeymoon destination - and a muscular marketing and publicity operation.

Disney World's attendance slumped somewhat last year, but analysts attribute that to an exceedingly strong 1987. And Disney's percentage decline was smaller than those of most other major attractions.

Meanwhile, Disney's expansion plans leave competitors searching for ways to keep their own turnstiles spinning.