The City of Light, pleading poverty, last month backed down from the 1989 World's Fair with which it was to celebrate the bicentennial of the French Revolution. But President Franc,ois Mitterrand still has $225 million earmarked for what he hopes will be "one of the major architectural events of the late 20th century"--a second Paris opera house for the historic, if lackluster, Place de la Bastille, where it all began in 1789.

The president himself will be the final judge of the $500,000 international competition for the opera's design.

Of the 750 proposals submitted to the jury--in sealed cardboard cylinders identified by number, not by name--as many as 30 may win prizes. But only the top six have been sent to the Elyse'e Palace for Mitterrand's decision, which has been expected "any day now" since Bastille Day, July 14.

The face of Paris has been changed by ambitious urban projects since the 1850s when Napoleon III ordered Baron Haussmann to send leafy boulevards slicing through the city. Projects built during the term of the late President Georges Pompidou include the massive Tour Montparnasse, the forest of skyscrapers at La De'fense, and the controversial--though successful--Pompidou arts complex whose nontraditional design was also selected in an international competition.

So it was not surprising that early in his presidency Mitterrand announced a slew of projects: a science museum, a concert hall and a national musical conservatory for the park at Porte de la Villette; an underground expansion of the Louvre (whose design team will include America's I.M. Pei); and a vast sports stadium nearby at Bercy.

The 23-person jury for the opera competition included composer Pierre Boulez, American architect Robert Venturi and Massimo Bogianckino, director of the other Paris opera at the gilt-and-gingerbread Palais Garnier.

The new Paris opera will occupy the site of the leaky, long-abandoned Bastille station, although Boulez and others had once hoped it might rub shoulders with the orchestral hall at the La Villette complex.

Though drawings of the six designs still being considered are not to be made public before Sept. 8, details of some of them have emerged.

One juror, Dennis Sharp, the British architect and critic who was indiscreet enough to publish an account of the judging process in the London Guardian, revealed that the the highest scores were given to a "postmodern pavilion-type project" with stepped sides. Another juror compared the plan to "a machine dropped on the site."

It is known that some of the plans propose a radical redesign of the Place de la Bastille. One of the designs suggests a walkway through the opera to bring pedestrians into the complex. Another takes as its motif inverted glass cones with one, sliced in two, fronting the square while the other, behind, houses the auditorium. At least one of the designs is in the running only for an honorable mention: It is said to be unbuildable.

Operation Opera-for-the-People is aiming to strip an elitist pastime of its antiquated trappings. After all, the reasoning runs, the Palais Garnier has to turn away two of every three potential customers. Hordes of them, hoping for a chance to buy returned tickets, wait on the steps before every performance. So why not encourage an audience that has shown such interest in opera on television, in Verdi records and in such films as Losey's "Don Giovanni" and Bergman's "Magic Flute"?

The old opera, though a distinguished a piece of urban sculpture, has its drawbacks. When Charles Garnier designed it for Napoleon III in the 1860s, he admitted unashamedly that his chef d'oeuvre was built to show off the ladies. The entr'actes, or intermissions--the flights of marble stairs, the rustle of silk, and the gentlemen who came to give bonbons to the dancers--were what mattered most to Garnier.

"It was a different world," says Franc,ois Bloch-Laine', 71, the head of Mission Opera-Bastille. He shudders to remember the invitations that used to come in the 1920s from a rich aunt who had a box at the opera: "They were endlessly playing a terrible 'Faust' in those days."

After World War II, Garnier's extravaganza struggled with funds shortages, bad management and recalcitrant unions. Bloch-Laine', then a finance ministry official, was called upon in 1976 to head a commission investigating its problems. He concluded that the only solution would be to start afresh.

When he was called back from retirement last year by the socialist government, things hadn't changed much. Despite its bronzes and gold paint, the Palais Garnier has no room for storing scenery. Most rehearsals have to be conducted in the suburbs, and sets have to be shipped in from workshops elsewhere in the city. Nearly 500 of its 1,900 seats, in the gods and in the boxes, have obstructed views.

Still, 333,000 people attended 170 performances (105 opera, the rest ballet) during the 1982 season. Of the $37.5 million budget for the season, $31.1 million was provided by the state, which brings the subsidized cost of each plush seat to $87.50 even though customers paid between $50 and $62.50 for a good seat.

It is believed that, with the same budget, the new opera will serve three times as many spectators: 1 million a season. And flexible scenery facilities in the new building will permit frequent alternation of productions--whether classical opera, operetta or modern works--in series over three or four consecutive nights.

That is out of the question at the present opera, and that explains the limited number of its productions. The unwieldy set of this season's "Otello," for instance, could not easily be dismantled, though singers need to rest their voices at least every other day.

Bloch-Laine' acknowledges that the tentative schedule--relocation and demolition finished by the end of 1984, and construction for 1985-87--cuts things a little fine. There is also the question of finding enough singers to perform at the new high-capacity opera house. "The star system will have to go," he says. "And one can't hide the fact that France isn't exactly a nation of musicians. We start on a basis different from that of Berlin or Milan."

Another problem with the Palais Garnier is that it makes no concessions to television cameras. The new opera will cater to home audiences watching cable television in Lyons and Marseilles. Bloch-Laine' hopes that by the time the opera is built, large-screen technology will be perfected to the point that the evening's show might be projected on the opera's exterior for passers-by in the Place de la Bastille.

"It will all help," he points out, "to justify the taxpayer's contribution."

His small team talked with opera directors in Sydney, San Francisco and Stuttgart, West Germany, before drawing up the program. The auditorium, it was decided, would be limited to 2,700 seats. New York's Metropolitan, the world's largest opera house, has a thousand more; but its size rules out all but the most powerful voices. And from the cheapest seats, almost 60 yards from the stage, according to Ge'rard Charlet, the team's architect, "the stage becomes like a screen, not a lived experience." At the Bastille, no ticket-holder will be more than 40 yards from the stage.

The team's program for the interior calls for five offstage storage spaces for sets. Modern opera houses on the Bayreuth model have three, arranged in the shape of a cross. "The Germans are kicking themselves now," says Bloch-Laine', "because they missed the chance to build these advantages into their new opera houses after World War II."

Another feature called for is a subsidiary auditorium into which sets can be wheeled from the main one. It will have an identical stage but room for only 1,700 spectators, and it will be used for rehearsals and filming as well as for performances of small-scale works.

The program calls for workshops, makeup rooms and studios where musicians, individually and in small groups, as well as full orchestras, may practice. The new opera also will have restaurants, cinematheque and shops selling records and sheet music. "The opera shouldn't be a forbidding place that opens only at 6 p.m.," says Charlet. "It should draw people in."

The detailed program Bloch-Laine''s team developed--and the additional constraints imposed by the tadpole-shaped site--nearly suffocated the architects' propositions, said juror Sharp.

The site in central Paris is well-served by bus and Metro. The opera, the new stadium at Bercy and the new finance ministry buildings at the Gare de Lyon are expected to do much for the rehabilitation of the city's eastern districts.

Sharp says the jury quickly realized that the combination of demands almost suffocated the architects' propositions.

The Place de la Bastille--framed by some six-story Haussmann buildings with late 19th-century frills and some plainer 17th- and 18th-century structures--was not planned very carefully. The vast cobbled intersection focused on the July Column (which commemorates those who died in the revolutions of 1830 and 1848) challenges an inspired piece of town planning. "It's like the medieval problem of building a huge cathedral in the center of a town," says Charlet.

The president's delay in announcing the winner of the competition indicates the choice has been difficult.

Meanwhile, isolated sallies against the project have been fired in the press. One architect writing in Le Quotidien de Paris claimed that what he called "new techniques" could expand the capacity of the Palais Garnier. It was argued with more foundation in Le Monde that the planned demolition of a row of dog-eared hotels and houses--described in the mission's brochure as "banal, not to say mediocre" and as giving a "ragged" air to the square--would mean the destruction of one of the last corners of old Paris.