Thirty years ago, in a burst of postwar puritanism, France shut down its brothels -- but without outlawing prostitution. So the world's oldest profession has continued to flourish here as thousands of its practitioners adorn bars, stroll the streets and even cruise the town in cars.

But a conservative member of the legislature, contending that necessity supersedes morality, has just proposed that whorehouses be reopened -- and his bill is stirring up the kind of controversy that spices conversation in Paris.

Joel Le Tac, the Gaullist who has introduced the legislation, argues that present-day prostitution has gotten out of hand, thus contributing to a rise in crime and venereal disease, not to mention tax evasion. In his estimation, Frenchmen spend the equivalent of $2 billion per year on hookers, without a sou of it going to the government.

Le Tac submits, therefore, that the legislation of bordellos will make the business easier to control, eliminate the gangsters who largely run it, and curb venereal disease through strict medical supervision.

Surprisingly, the majority of French seem to support his view. In a recent opinion poll published in Le Figaro, the Paris newspaper, 65 percent of respondents said that they were "rather favorable" to the revival of brothels.

Le Tac is backed as well by Marthe Richard, now 89, the woman politician who vigorously promoted the law that closed bordellos in 1946. She has changed her mind since then, she says, because brothels now can be better managed.

On the other hand, Le Tac's proposal is opposed by a wide spectrum of adversaries, ranging from police officials and local mayors to fellow legislators and partisans of women's rights. Among his most vocal foes are prostitutes themselves, who appear to be nearly unanimous in their denunciation of his idea.

Mayors are against Le Tac's plan, since they do not want the responsibility for regulating brothels in their towns. As the mayor of La Rochelle says, exaggerating for the sake of emphasis: "I have no intention of becoming a pimp."

A member of the Paris Municipal Council calls the project impractical simply in terms of the space it would require. He calculates that there are 40,000 prostitutes in France, half of them in Paris, and if each brothel housed an average of 20 girls, 1,000 bordellos would have to be opened.

These statistics are significant, since they reveal the extent to which prostitution has proliferated since whorehouses were banned. In 1946, there were 7,500 registered prostitutes in Paris, about 1,300 working in brothels. Thus the Parisian prostitute population has tripled in a generation.

The prostitutes, meanwhile, have organized an energetic lobby to fight against the resurrection of brothels, and they have even petitioned French President Valery Giscard d'Estaing to help them.

Their current action is reminiscent of demonstrations they staged in 1975 against police pressure. An official study conducted then recommended that prostitutes be given the status and social benefits enjoyed by other selfemployed workers, and it ruled out the reopening of bordellos.

In their present protest against Le Tac's proposal, the girls claim that brothels violate their civil rights. One veteran, 55-year-old Gaby, explained to me:

"It was like being up in jail.We had to stick to regular hours, and we couldn't select our clients or fix our prices. Today a woman can work for herself, without sharing her fee with a madam or a pimp, and she can choose her customers."

Prostitutes also deny they are a major source of venereal disease, and their assertion is borne out by official figures that show that roughly 85 percent of the cases of syphillis and gon- orrhea are caused by amateurs.

Moreover, those who remember the bordellos of the past recollect that they were hardly models of hygiene, since girls often were contaminated between medical check-ups. Or, as one former madame says: "You won't do anything for public health unless you turn brothels into hospitals."

As for the contention that bordellos will serve to reduce the crime element in prostitution, many specialists on the subject are unconvinced.

Though the old brothels were run in orderly fashion, often by underworld syndicates, their shutdown did not increase the role of gangsters in the profession. Instead, many girls went into business for themselves, thereby eluding the control of both the police and pimps.

But probably the strongest argument against bringing back brothels is that the nature of prostitution has undergone a transformation within the past decade or so.

Whores are no longer recruited from the ranks of innocent peasant girls, unwed mothers or jilted sweethearts. Many are housewives or secretaries who function on a parttime basis to earn extra money, and they have no desire to be assigned to brothels. Or as Barbara, the 30-year-old daughter of a government official puts it:

"The idea of municipal sex clinics is absurd.The Germans may have their famous Eros Centers, but they've always liked living in barracks. We're in France, and that means freedom."

One question, in France as elsewhere, is why prostitution survives at all in the face of a sexual revolution that has been eroding the double standard of morality.

The answer, here at least, is that prostitutes exist for middle-aged businessmen, provincial visitors and tourists who cannot easily meet amateurs in discotheques. And perhaps more important, professional prostitutes assure discretion for the married man.

With all this, however, bordellos evoke a certain nostalgia for turn-of-the-century opulence, and though they may never be reopened here, the present debate about them has cast Parisians into a romantically naughty mood.