he last time Chicago tried to celebrate the anniversary of Christopher Columbus' discovery of America, the party was a year late. This time around, the city is taking no chances.

A group of Chicago civic leaders and businessmen is laying plans for a World's Fair to commemorate the 500th anniversary of Columbus' discovery. Unlike the 1893 Columbian Exposition, this one is running on schedule, with an opening set for mid-April 1992. Banners bearing the fair's logo and the slogan "Age of Discovery" are already flying from some city buildings.

The Bureau of International Exhibitions (BIE), the Paris-based international body that sanctions world's fairs, gave tentative approval in June for the fair, the first major exposition held in the United States since the 1964-65 New York World's Fair (this year's fair in Knoxville is classified as a regional fair, roughly one-fifth the size of a world-class exposition).

If the BIE gives final approval to the fair later this year, Chicago officials expect construction to begin quickly on the 500- to 600-acre site for the fair on the city's Lake Michigan shoreline, a $1 billion project that will include the creation of a 180-acre man-made island adjacent to McCormick Place, the city's jumbo convention hall.

In a recent story on the fair plans, Crain's Chicago Business, a local business publication, said Chicago "has not faced a single greater physical challenge since Mrs. O'Leary's cow invented urban renewal."

Indeed, Chicago officials hope the fair will work a kind of urban renewal on the city's lower lakefront and South Loop areas. Parking and support facilities, they hope, will revitalize blighted areas near the site, while the project will create thousands of jobs badly needed by Chicago's depressed economy.

"This can do nothing but improve Chicago," Mayor Jane M. Byrne said after the BIE announced its tentative approval of the fair proposal.

In a city where vehement political opposition can be drummed up for almost any issue, the fair proposal has met with virtually unanimous approval in Chicago. What opposition has cropped up so far has come from environmentalists concerned about the effect of the project on the lake's ecology, and from some politicians worried that planning for the fair have been moving along without enough input from the public.

"My fear is that it's going to be one of those Robert Moses kind of things," said City Council member Martin Oberman, invoking the name of the planner of the financially unsuccessful 1964-65 New York fair. "It may be a terrific thing, but nobody's laid out yet how it's going to be done."

Roger Seitz, a partner in the architectural firm of Skidmore Owings & Merrill, says the relative lack of opposition to the fair is "surprising" compared with the kind of objections that have arisen in the past over major city projects, such as the planned revitalization of Navy Pier and the ill-fated Crosstown Expressway. "When I worked on the Crosstown, I could take credit for the election of two aldermen and the creation of three civic groups," he said.

Seitz is part of an ad hoc committee of Chicagoans who have been working on the fair proposal for the past 18 months, a virtual Who's Who of the city's business, civic and media leadership. With $500,000 in funds donated by businesses and an estimated $1.5 million in gratis professional services -- such as Skidmore Owings & Merrill's architectural plans -- the group put together a proposal to the BIE and now is laying the groundwork for the actual construction of the fair. Chicago's contentious trade labor unions have even pledged to keep fair construction free of strikes and other labor problems.

Despite the BIE's provisional approval of the fair proposal, however, Chicago's plans still face competition from other bidders for fair dates. The BIE tries to space out major fairs so that they will occur roughly a decade apart, a policy that raised immediate problems for Chicago from Paris, which desired a 1989 fair to commemorate the French Revolution.

That conflict was solved by a compromise arranged by the U.S. and French governments that will let both cities have major fairs despite the three-year gap, a plan favored by the BIE. But Chicago now faces last-minute competition from Seville, Spain, and Miami, which also wish to celebrate the Columbus anniversary.

Chicago officials are trying to iron out those problems, bringing up the possibility of a "Columbian Year," with regional fairs at Seville, Miami, and Columbus, Ohio, perhaps, as adjuncts to the larger Chicago exposition. "Our feeling is there should not be a loser," said Donald A. Petkus, a vice president of Chicago utility Commonwealth Edison who is serving as vice president of Chicago World's Fair 1992 Corp. and has supervised much of the preliminary planning for fair.

So far, Seville officials seem willing to negotiate, Chicago sources say, but Miami has remained intractable.

Petkus believes that Miami's bid is futile unless it wrests federal government support away from Chicago, and he says that's unlikely, "unless they come up with something clearly spectacular. And clearly spectacular would mean doing it on the moon or something."

Chicago isn't promising the moon, but it is offering its lakefront, the site of the 1893 Columbian Exposition and the 1933-34 Century of Progress Exposition. The latter produced a 72-acre man-made island that is now the site of Meigs Field, a small airport largely used by corporate aircraft. That field is set to be closed and the land incorporated into the 1992 fair, under the current plans.

On that land, the new island, and lake-front property, Chicago hopes to set up an international exposition with all the fixings: a Boulevard of Nations, an Avenue of Industry, a Circumfrential Air Train, a Synchroveyer Transit Line, and amusement park rides.

Chicago officials think they can pay the fair's billion-dollar price tag out of admissions receipts. "The financial strategy is to basically marry the attendance, the ticket price and the capital expenditures to come out even in the end," Seitz said.

"The revenue part really isn't a problem," Petkus said, "unless it rained for 150 days or Lake Michigan rose 20 feet."

The planners expect that 54 million people will pass through the fair during its six-month run, a 300-000-a-day clip, and were encouraged in their attendance projections by the fact that 500,000 people showed up over the Fourth of July weekend for Taste of Chicago, an annual sampling of the city's restaurants set up in Grant Park, near the proposed fair site. "If they can get half a million people to what was basically a collection of hot-dog stands, we can do well on attendance," Seitz said.

Under the current plans, the Chicago world's fair corporation would sell bonds in mid-decade to raise construction funds. The bonds would be paid off after the fair from gate receipts and other income. Some of the more optimistic planners are already giving thought to uses for a possible surplus.

Still, most world's fairs have turned into colossal money-losers, and officials concede they will probably have to find some guarantor for the bonds. "Let's face it, it has to be a governmental entity," Petkus said.

Such risks worry some Chicago politicians, who are also concerned that the city not become committed to making a lot of expensive public works improvements solely to benefit the fair. Fair planners, however, insist that the improvements they are seeking from the city -- notably expansion of expressways near the fair site and a lake-front mass-transit system -- would eventually be built anyway.

In addition to hastening those projects, the fair's proponents say, the exposition would also speed up development in the South Loop and Chinatown areas by providing a vote of confidence in the areas' future. "It gives everybody a focus and it's an expression of confidence and public spirit," Seitz said.

Still, says Petkus, the lake-front site was chosen because "we think it's the showplace of Chicago. We're not trying to make people buy a ticket to an urban renewal project."

When the fair is over, the planners hope, Chicago will be left with a new expanse of public parkland, plus the transit line and any other improvements built in connection with the fair.

First, though, Chicago has to secure final approval for the fair from the BIE. But at least one potential exhibitor is already itching to begin building its pavilions. "Japan's ready to go," Seitz said. "They just want to know when we're ready to talk."