Men who enjoy soft-core sexual fantasy might give the World Wide Web site for Playboy magazine a rating of 10.

But according to the Recreational Software Advisory Council, the Playboy Web site is actually an 11. That's four points for nudity, four points for vulgar language, three points for depictions of sexual activity - and a zero for violence, because the Playboy site doesn't have any.

Cambridge-based RSAC has developed a system for rating Web sites, a system that RSAC executive director Stephen Balkam hopes will stave off calls for government censorship of the Internet.

``I have two children, and I'm very concerned about some of the stuff I see on a day-to-day basis'' on the Internet, said Balkam. ``What we've tried to do is to walk a fine line and a balance between being pro-free speech, which we definitely are, but also pro-parental choice.''

The RSAC system relies on a special Internet protocol developed down the street at MIT. PICS, or the Platform for Internet Content Selection, is a system that allows companies and organizations to add ratings tags to Web sites.

But the big difficulty in rating a site is deciding whose standards will apply. A member of the Christian Coalition will find one sort of Web site offensive; a member of the Fund for a Feminist Majority will be disturbed by very different material. Whose values will be applied?

RSAC's answer is to have the Web site operator rate his own site, using a questionnaire that can be filled out at the RSAC Web site. The organization worked with Donald Roberts, a professor of communications at Stanford University, to draw up a set of yes-and-no questions to determine the nature of the materials on hand. For example: ``Does your content portray any passionate kissing, clothed sexual touching, nonexplicit sexual touching, explicit or nonexplicit sexual acts, or sex crimes?''

The RSAC questions are detailed, and sometimes dismaying. But they can offer a distinctive profile of the Web site. And the site operator is the one who answers the questions, not a professional Web screener who might spend a mere five or 10 minutes at the site.

The questionnaire is instantly graded by a computer, which uses a mathematical formula to determine how the site rates in four categories - nudity, sexual activity, harsh language and violence. RSAC then sends the Web site operator a tag containing the site's new rating. This tag is simply added to the top of the site's home page. It's invisible to anyone reading the page, but not to browsing or screening software designed to recognize the tags.

The Microsoft Internet Explorer browser automatically recognizes the RSAC ratings. A parent who uses this browser can set it to block any site that contains a lot of sex or violence, or he can block out any site that has not been rated. But by typing in a password, the parent can visit any location on the Web, no matter how raunchy. The leading browser maker, Netscape Communications Corp., plans to add RSAC ratings to a forthcoming version of its Navigator browser.

The RSAC approach is also being adopted by blocking software makers like Microsystems Software Inc. of Framingham. The company's Cyber Patrol software contains its own built-in list of possibly offensive Web sites. But the newer versions of Cyber Patrol also check every Web site for its RSAC rating.

So far, only a tiny percentage of Web sites actually have RSAC ratings. But Balkam expects the system's popularity to grow, as an alternative to censorship of the Internet. The on-line service CompuServe has agreed to use the RSAC standard for all the materials it carries, and the Web site design company USWeb, which designs sites for clients like Hewlett-Packard, Lotus and Phillips Petroleum, has done the same.

``It's far preferable to some government agency trying to sit down and decide what is or is not appropriate for children,'' Balkam said.

He admits that users of his system could lie about their content, thus making a sexually explicit site available for children. But Balkam said that RSAC will patrol the Web in search of such violations. Companies that post fraudulent RSAC ratings could be liable to legal penalties for fraud.

Balkam also thinks that RSAC's self-rating approach is ideal for the television industry, which is trying to design an electronic system to attach sex and violence ratings to every show. Rather than have a screening committee sit through thousands of hours of TV shows, a producer could fill out a questionnaire for each episode, and have the show automatically rated by a computer.

``Certainly our system is very, very adaptable,'' said Balkam, ``and I feel it could be very successfully utilized by the television industry and, in my wildest dreams, the movie industry too.''

Hiawatha Bray is a member of the Globe staff. He can be reached by e-mail at Bray@globe.com.

This story ran on page E4 of the Boston Globe on 07/25/96.