ROME -- Francesco Santandrea's afternoon tryst in the home of one Mrs. Nicoletti turned out to be a major setback for Italian lovers.

Not that Santandrea, 40, did anything unusual, apart from being caught, so to speak, with his trousers down. Such things happen in a country where seduction is a noble art.

His problem was that he became a legal precedent. And his fate sent shock waves rippling down the spines of many a similar sinner after the supreme appellate court last month upheld his six-month jail sentence for having violated a family home in the absence of the husband.

The court also ruled that Mr. Nicoletti was fully justified in seeking damages from Santandrea in a civil case.

Perhaps the days are over when Italian courts acquitted enraged husbands who shot lovers caught in flagrante delicto with their wives. But the court ruling revived Article 614 of the penal code, known in popular jargon as "the law to safeguard cornuti," as cuckolds are called.

Cuckoldry is common in Italy. But Santandrea's case is sure to change the methods of those Casanovas who for centuries have climbed through windows and slipped through back doors as husbands walked out the front.

In its four-page explanation, the court ruled that the penal code classified the matrimonial home as sacrosanct. Therefore, "he who sneaks into such a home during the absence of a husband, with the intention of having carnal relations with the wife, has to be considered a person committing an act of violation against the will of the husband," the court wrote.

It said this rule also applies to a mistress who enters the home of a married man in the absence of the wife and without her consent.

"From now on, any lover who wants to avoid a trial must have a written statement from all members of the household saying that he or she is allowed to enter the house. Otherwise the law will consider it a clandestine entry," said a leading criminal lawyer in Rome.

Santandrea's case goes back to 1983, when, on a sunny day in May, Mrs. Nicoletti's husband returned unexpectedly to his home in the town of Trebisacce, near Cosenza in southern Italy.

Noting that his wife was not alone in bed, Nicoletti did not take out his shotgun but walked down to the local judge and swore out a complaint. The judge had the lover arrested and a regional court sentenced him to six months in jail.

Santandrea's protests against what his lawyer called "a miscarriage of justice" went all the way to the top appeals court.

The Santandrea case is not unique.

Three years ago, the same court upheld the case brought against a teen-ager caught in bed with a girl at home in the absence of her parents. A year earlier, the court ruled that two lovers found in bed by the child of one of them could be sentenced to as many as three years in prison for corruption of a minor.

The Italy of the 1980s may not be a hospitable place for the imitators of Giovanni Jacopo Casanova, the 18th-century Venetian adventurer whose name became a symbol of seduction.