PARIS -- Among Parisians trapped in the city's heat this month, the usual hot topics are the season's bru~lant fashion -- midwaist Eisenhower-style evening jackets; the "in" bistro, Bofingers; or this year's drink nouveau, Brut de pe~che (peach champagne).

Among the tourist army in annual encampment, however, the hottest topic is a tour best described as "breathtaking" -- Les Egouts de Paris -- the sewers (it does sound better in French) of Paris.

Parisians officially classify the stroll through 200 meters of working, dripping, Left Bank culvert a curiosite', like the city catacombs or dog cemetery, rather than an attraction. The distinction is made, one imagines, to avoid confusion with the Louvre and other Parisian landmarks whose admission prices are substantially higher than the 8 francs ($1.35) charged for admission to what is, in effect, an Ed Norton dream.

Admittedly Paris' sewers are unique -- hundreds of miles of primordial canals and arched stone tunnels deep below its streets, that have evolved over 600 years. Channels within this maze direct a gravity flow collector system that slops waste from house and street drains into larger drains, galleries and collector basins into a great gray-green greasy underground river beneath the city. It's said the system is so vast that waste-bearing water coursing from the city for purification passes under the Seine an average of four times before finding its way into the river. The tunnels also house Paris' fresh-water pipes, telephone cables, pneumatic mail service and traffic control system, plus the dank atmospheric allure that inspired Victor Hugo's sewer-commuting hero, Jean Valjean of "Les Mise'rables" -- and the world's most famous subterranean organist, "The Phantom of the Opera."

The currently hot musicals based on both stories appear to have contributed to the popularity of the sewer tours, which are offered between 2 and 5 p.m. on Mondays, Wednesdays and the last Saturday of each month, except in times of heavy rainfall.

This summer, it's not unusual to find 100 persons or more lined up an hour before opening at an entrance near the Eiffel Tower distinguished only by two small signs and a raised 10-foot steel grate. Sharing umbrellas, they chat, peering down the chain-barred entrance stairway as subterranean noises echo upward. A few minutes before 2 p.m. an e'goutier dressed in the traditional dark blue smock of Paris sewermen emerges molelike and squints at the crowd. This summer, he says, demand for the tour has been, frankly, "capacity straining."

"A couple of things bring me here," says a Cornell University student named Richard, citing interests in architecture and urban planning as well as a "kind of a familiarity" with "Les Mise'rables." "But mostly, I'd say I've a penchant for visiting the weird and novel in each city.

"In Rome, for example, I went to the Church of the Immaculate Conception," he says, producing a dogeared postcard from his duffle. "That's the cre`che where the monks collected bones and skulls of their brothers."

"I got interested from the movie of 'Les Mise'rables' on television a couple of years ago," says Joe Powers of Champaign, Ill. "Also I've read that Harvard puts their new students on a tour of Boston sewers so they'll understand how a city runs."

Pamela Previte of Houston says she learned of the tour by "word of mouth," as do most visitors. Tourism agencies and authorities tend to treat the sewer system as if it were beneath them. "I used to live here," Previte explains, "and I've been told it's really good. Especially by French friends and students who do it themselves -- pop a manhole, go down into the sewers, stay all night and have picnics! It's sort of a traditional thing they do here."

Following the tradition, visitors to Les Egouts descend several stairs to find themselves in a long, narrow, well-scrubbed cavern buttressed by the massive stone block of a Seine retaining wall. A smooth concrete floor moistly echoes constant bubbling sounds from open canals down where the cavern narrows and disappears into dark tunnels. Endlessly humid, dank and dim, it's the ideal place for a torch concession.

The cavern adjoins a tidy exhibition gallery whose photos and drawings highlight the history of Paris' waste management -- with sort of a "Great Moments in Trash" motif.

"A sewage museum," Sam Johnson from Fort Myers, Fla., says to a friend. "Now isn't that novel?"

After a few minutes, visitors are hurried into the museum's audio-visual theater, a rather informal affair of chairs and curtains at the tunnel's end, where a fuzzy, 12-minute slide presentation is shown.

No chief witness before a congressional committee ever danced as lyrically about or around a subject as the ebullient narration does about ... waste. While bright scenes of above-ground Parisian life flash by to the accompaniment of an airy '50s jazz score, the narrator pours forth a blizzard of statistics concerning the number of Parisians "making 5.5 million phone calls to ... buy 3 million loaves of bread ... and 1,000 tons of shellfish ... while taking so many baths each day." A nude bathing blond flashes briefly on the screen to recapture flagging interest as the narrator concludes, stentoriously, "... and all of this, of course, creates a considerable amount of ... WASTE!"

Roughly enough cubic waste, explains a second, softly accented narrator as a cartoon slide appears, "to equal in height the second story of the Eiffel Tower." She then graphically details the role of the e'goutiers in preventing this rather obtrusive-looking edifice from being built each day. Drifting occasionally into the same flood of facts as her predecessor, she mentions the 26,000 manholes and "1,300 miles of sewers {that} equal the distance between Paris and Istanbul," before ending the show with another hymn to "Paris, the city which sings above a dim, humid world below."

But the pie`ce de la re'sistance beneath La Place de la Re'sistance lies at the far end of the tunnel where a narrow towpath snakes along several roaring, functioning canals before trailing off into grisly, echoing darkness. Here, guides thread visitors along a six-stop, floodlit journey amid a labyrinth of pipes and pathways. The atmosphere is steamy and steeped with tradition. Strange groaning and clanking sounds emanate from some rusting hulk of subterranean pipe below, "where work is dangerous due to the darkness, the damp and the quantity of ... water," a loudspeaker intones over the noisy, liquid rush.

"The original 'eau de toilette,' " Johnson declaims, backing around a catacomblike corner, before encountering another tour highlight -- an eight-foot-high steel ball "stopper" that e'goutiers roll into canals to plug them against the tide. Wine bottles, jars, car parts, furniture, household appliances, "even whole bicycles," that clog the system's drains and screens must be removed regularly. As the film takes care to note, "you can find anything in the sewers of Paris."

The engineer Belgrand designed most of the system beginning in 1853 during Haussmann's reorganization of the city boulevards. It was inaugurated in 1863 with a grand tour for the appropriate ministers, who were, so the Egouts museum suggests, appropriately impressed. Subsequent tours became fashionable among citizens who began the 125-year-old tradition of not only using, but visiting their sewers.

Over the years, the popular subterranean world of dark dancing waters acquired a small electric tramway. That "drain-train" eventually yielded to boat rides upon the effluvial backwash beneath Place de la Concorde and the Tuileries. Fourteen years ago, when the strong-hearted pleasure of punting the flow had lost much of its appeal, the city inaugurated its current walkthrough facility.

After 26 years as an e'goutier and guide, Jean Roux is not surprised by the underground interest. "This museum is more popular than the old boat rides. Tout le monde visits now," he says. "English, German, American, Italian, Japanese ... Everyone knows Jean Valjean!"

"The Phantom of the Opera," he smiles, "doesn't live down here. He's just a fairy tale."

"Le fanto~me is make-believe," another e'goutier selling post cards exclaims. "Only a made-up story." But ...," he adds proudly, "Jean Valjean ... he was real ... He lived in the sewer!"