LOS ANGELES >> At the end of “;Manhattan,”; the celebrated movie romance from 1979, a teenager played by Mariel Hemingway delivers some good news to the 42-year-old television writer, portrayed by Woody Allen, with whom she has had a long-running sexual affair.

“;Guess what, I turned 18 the other day,”; said Hemingway, in what was framed as a poignant encounter. “;I'm legal, but I'm still a kid.”;

That was then.

Roman Polanski's arrest on Sept. 26 to face a decades-old charge of having sex with a 13-year-old girl stirred global furor over both Polanski's original misdeed and the way authorities have handled it—along with some sharp reminders that, when it comes to adult sex with the under age, things have changed.

Manners, mores and law enforcement have become far less forgiving of sex crimes involving minors in the 31 years since Polanski was charged with both rape and sodomy involving drugs. He fled rather than face what was to have been a 48-day sentence after he pleaded guilty to unlawful sex with a minor.

But if he is extradited from Switzerland, Polanski could face a more severe punishment than he did in the 1970s, as a vigorous victims' rights movement, a family-values revival and revelations of child abuse by clergy members have all helped change the moral and legal framework regarding sex with the young.

Polanski's lawyers—including Reid Weingarten, a Washington power player—are likely to argue that Polanski does not even qualify for extradition from Switzerland, because he was set to be given a jail term of less than one year when he fled to France in 1978.

But Stephen L. Cooley, the Los Angeles County district attorney, has signaled that he believes much stiffer penalties may be in order. Questioned by reporters just after Polanski's arrest, he said the filmmaker had received a “;very, very, very lenient sentence”; that “;would never be achievable under today's laws.”;

In 1978, officials argued that the plea agreement would spare Polanski's young victim the notoriety of a trial. But the soft deal was also in tune with the more permissive times, when sex with the under age was often winked at, especially among entertainment world sophisticates.

“;The sort of thing that would get guys arrested now was very common back then,”; said Michael Walker, who made a study of the Los Angeles sex-and-drugs scene for his 2006 book, “;Laurel Canyon: The Inside Story of Rock-and-Roll's Legendary Neighborhood.”;

Polanski was treated by authorities, including Judge Laurence J. Rittenband, not so much as a sexual assailant but as someone in the mold of Isaac Davis, Allen's character from the movie “;Manhattan”;: that is, as a normally responsible person who had shown terrible judgment by having sex with a very young, but sophisticated, girl.

Contemporary reports in The New York Times and elsewhere captured a whiff of that attitude. In one article by The Associated Press, published in The Times on Sept. 20, 1977, Rittenband scolded Polanski for taking advantage of his victim even as he was “;noting the teenage girl 'looks older than her years' and was sexually experienced.”;

A 28-page probation officer's report completed in September of that year presented a broadly sympathetic portrait of Polanski and his behavior, even while acknowledging that the victim, Samantha Geimer (who has since publicly identified herself), had offered grand jury testimony of forcible rape.

Submitted by the acting probation officer Kenneth F. Fare, and signed by a deputy, Irwin Gold, that report, which recommended against further jail time, said “;the present offense appears to have been spontaneous and an exercise of poor judgment by the defendant.”;

In a further conclusion that appeared to shed blame on the victim, it said, “;There was some indication that circumstances were provocative, that there was some permissiveness by the mother,”; who had allowed Geimer to spend time with Polanski. And, in a conclusion that might particularly jar readers today, it pointed toward evidence “;that the victim was not only physically mature, but willing.”;

The probation officers quoted a pair of psychiatrists as saying that Polanski was not “;a pedophile”; or a “;sexual deviate.”; And in an extraordinary bow toward his reputation as a filmmaker, and the supposed difficulty of adjusting to life in the United States, the report said:

“;Possibly not since Renaissance Italy has there been such a gathering of creative minds in one locale as there has been in Los Angeles County during the past half century. While enriching the community with their presence, they have brought with them the manners and mores of their native lands which in rare instances have been at variance with those of their adoptive land.”;

Both the law and sentencing practices have changed since Polanski was arrested. Robert Weisberg, who teaches criminal law at Stanford University's law school, said Polanski would face a stiffer punishment now, even for the single unlawful sex charge.

“;If he were sentenced for just that crime today, a good prediction would be he would get three years in state prison,”; he said.

A shift toward determinate sentencing, Weisberg pointed out, has sharply reduced the ability of judges to impose lighter punishment, while strengthening the resolve of prosecutors who, in a case like Polanski's, cut tougher deals because they are backed by heavier and more definite sentences for each count, and a lessened opportunity to get probation. Moreover, Weisberg said, the consideration of Geimer's attitude and sexual history—which she was asked about during her grand jury testimony—would be almost unthinkable.

“;It's ghastly to think this could have happened with a 13-year-old,”; Weisberg said in a telephone interview this week. But even with older victims, he said, “;it is much harder for a defendant to undermine the complainant on the basis of past sexual history.”;

Joelle Casteix, the southwest regional director of the Survivors Network of Those Abused by Priests, traced the changes in attitude toward sex with minors, among other things, to a change in the movies.

“;The kids of the '70s were raised with films—'The Omen,' 'The Demon Seed'—that put adult sensibilities into children,”; said Casteix, whose group called last week for continued pursuit of Polanski at a demonstration in Los Angeles. “;But a lot of changes in the '80s, the Reagan era, made people look at their kids a little more and realize they were children.”;

(”;An Education,”; a new film from the director Lone Scherfig and Sony Pictures Classics about the seduction of a 16-year-old by an older man, is set in long-ago 1962, and telegraphs distaste. In a review for The New York Times, A.O. Scott wrote that Peter Sarsgaard, who plays the seducer, allows “;doubt and then revulsion to mix, drop by drop, into our impression of him.”;)

Woody Allen, who cast himself as the older man in “;Manhattan,”; is among the Hollywood big names who have rallied around Polanski, signing a petition on his behalf. As for that movie, it remains unclear whether any studio today would make the film, with its matter-of-fact portrayal of an illegal dalliance—or statutory rape—intact.

“;I don't think there's an answer to that question,”; said David Picker, who as a United Artists executive was involved with the acquisition of Allen's project in the 1970s. “;It's a different world.”;