"How do you fit a rhinoceros into a hip bath?" the newspaper Le Monde was wondering the other day, after the results of the international architecture competition for a new Paris Opera at the Place de la Bastille were finally--if not definitively--announced.

The 745 entrants from around the world had wrestled with the problem of squeezing the complex machinery of a supermodern opera into a constricting site, and some had produced ingenious solutions. But President Franc,ois Mitterrand's word was that three of the six finalists recommended to him by an international jury in July would have to go back to the drawing board to develop their plans, construct models, specify building materials and report back at the beginning of October so he can make his final choice. The other three are out of the running.

None of the three finalist teams of architects is exactly a household name. All are relatively young, and as a group, they make up an exotic geographical cocktail: Carlos Ott, 37, a Canadian citizen, was born in Uruguay; Rocco Sen Kee Yim, 30, is from Hong Kong; and representing the Old World is a Paris-based group of two Romanians, Dan Munteanu and Teodor Georgesco, with a lone Frenchwoman, Odile Perreau-Hamburger.

Late last week, they and the three unselected finalists, all winners of 250,000 francs each, or $31,250, in prize money, converged on Paris, and to an audience that included a sprinkling of the 11 runners-up and the 45 honorable mentions, they explained how they envisioned a "popular opera" on this historic but architecturally undistinguished site.

In terms of prestige, the project is an architect's dream. "There are many operas in the world," said Ott, "but only one Place de la Bastille." The major problem was grappling with what Nicholas Hare, a British finalist, called "the very fierce conditions of the brief." Ott, who has worked on several commissions for the Canadian government, including a $50 million renovation on the Royal Ontario Museum in Toronto, was perhaps most successful in adapting his design to the auditorium and workshop plans spelled out by the Bastille's technical commission.

With the upcoming commission for a Royal Toronto Opera in the back of his mind, Ott built up a huge dossier on the Paris project on weekends and in his spare time. His stepped pavilion takes up the curves of the Place de la Bastille in a harmonious, unostentatious design, with a convex supplementary auditorium breaking up the site's long stretch along the Rue de Lyon. He respects the existing layout of the square and, unlike most other contestants, retains the 17th-century building on the northern corner of the site. "We've had enough of the urbanism of the bulldozer, the tabula rasa," he said in his explanatory speech, stressing that he saw the project in ethical as much as esthetic terms.

A second finalist, Rocco Yim, with his partners Patrick P.W. Lee and Bernard M.B. Hui, has been working on a range of commercial development projects (hotels, restaurants and offices) in Hong Kong, as well as two hotel projects in south and central China in collaboration with the Chinese government. The central feature of his opera proposal is a cylinder housing the theater, with, as a foyer, a glass-fronted half-cylinder facing the square "so that the audience finds itself on center stage even before it enters into the auditorium."

Yim visited Paris once, in 1976, and was impressed by the life on its streets. He would like, he says, for "even a common tourist with no knowledge of the history" to pass by and learn something. His design incorporates a pedestrian precinct he calls the "street of history and progress," which draws the public into the complex past rows of historical statues, and his interest in European history has thrown up a number of what he calls symbolical and metaphorical references: an unfinished stone wall with cell-like windows looking onto the place, symbolizing the destruction of the original Bastille prison; a neon-lit guillotine with distorted glass walls "to symbolize the terror and chaos" of the revolution; and a memorial court with three columns carrying the words "liberty," "equality" and "fraternity" in "all the languages of the world."

If Yim's version begins to sound more like a museum than an opera house, the two Romanians of the third team of finalists see things differently. The Place is a mess, architecturally speaking, says Munteanu. His partner, Georgesco, adds, "There's no sense in kneeling down before the past. The Place should evolve."

Munteanu came to Paris in 1981 from Bucharest, where he worked on the architectural staff of the Romanian ministry of culture. This meant, in addition to a slew of museums and houses of culture, designing two 700-seat theaters in the provinces and a smaller one for the Bucharest National Theater. His team's project turned the official specifications on their head. The jury liked its "theatricality," but described it to Mitterrand as unbuildable.

But it must have impressed the president and as it turned out, its Paris-based team includes one architect, Odile Perreau-Hamburger, who has worked for the French ministry of urbanism and housing. The design, which the architects say they are now having to rework a little, squares off the Place, turns the piazza of the Bassin de l'Arsenal, where the Canal Saint Martin goes underground, into the opera's forecourt, and feeds the audience in through an entrance off the Rue de Lyon. Its boldest stroke is an open-air amphitheater built onto the square, to be supplemented with tiered seats that could be wheeled outside from the opera. Munteanu points out that the maximum of 2,700 seats budgeted for in the original specifications for the opera isn't much in this day of football games and rock concerts. He would like to see room for major performances of all kinds at the Bastille.