It was the typical zany convention weekend, with free-flowing wine in the hospitality room of the Cliffside Inn here, prizes for the all-around best huggers, and kudos for Saturday evening's trivia champion.

Typical except for collective brain power, that is. The 67 participants, from the Washington metropolitan area and elsewhere in Maryland, were all members of Mensa, an international organization you can join only if you're smarter than the other 98 percent of us--and can prove it through your scores on one of a number of standard intelligence tests. In general, the minimum range for Mensa member IQs is 130 to 140, depending on the tests.

Sponsored by M-Broglio, a branch based in western Maryland, the weekend was the kind of social gathering that has become popular among the country's nearly 50,000 Mensa members. Donna Bachtell of Hagerstown, Md., M-Broglio's coordinater, said she works two part-time jobs to help finance trips to Mensa functions as far away as Michigan and Nova Scotia.

Most of the participants acknowledged without hesitation that they show up because they like to be with people like themselves. Though members range from welfare recipients to multimillionaires, said Washington metropolitan Mensa chairman Jim Lange, "Mensans can tell one another after a short conversation. You can tell, not who the Mensans are, but those who are eligible."

"You start talking shorthand to each other," added Cathy Merkle. "You share a different kind of sense of humor, a rapport that is difficult to find in other groups."

Or to put it more bluntly, as Cliff Johnson of Lexington Park did: "Most of my daily life I deal with very stupid people. It's nice to be with people I can relate to."

Though most of those at Harpers Ferry fit the description of the "average" Washington area Mensan (thirties to forties and childless), there were a few families in attendance, among them one that contained three generations of Mensans: Lucas Sawyer, 10, of Bethesda; his mother, Katherine DeWitt Jr., a member for 12 years and editor of the newsletter that circulates to the 1,600-member Washington chapter, and his grandmother, Katherine DeWitt Sr., who joined several years ago.

Most of the activities were definitely adult-oriented, from a two-hour guided tour of historic Harpers Ferry to the gathering's one and only serious speaker, Jean Green from Boonsboro, Md., a Mensan and antiques restorer who gave a talk on how to tell whether an antique is the real thing.

In between, there was a dinner, a brunch, an open house for new members and assorted games. Among them: Carnelli, a copyrighted word association game invented by Jan Carnelli, a member from Vienna, Va. After six rounds of Carnelli, the undisputed winner was Richard Arkin of Rockville, a lawyer for the Food and Drug Administration.

Jeff Landaw of Baltimore, a copy editor for The Baltimore Sun, walked off with the bottle of wine that was first prize in the trivia contest. Said David Hume, who founded the Washington-area Mensa group in 1962: "If you want to know some people with some weird talents . . . Jeff knows more unbelievably ridiculous things than anybody."

The Mensans were quick to point out, however, that membership in the organization of superbrights does not automatically mean success in the world at large. Chairman Jim Lange, 41, said he's "done about 20 jobs in 20 different categories," one of the most recent of which was laying bricks. The author of two unpublished novels, he graduated from law school at American University last May, flunked half of the bar examination, has just retaken it, and is currently seeking employment.

While most of the participants were there for the comradery, some were promoting the organization's special interest groups, called "SIGs"--the medium through which most Mensans meet each other. The Mensa organization has national and local SIGs for interests ranging from computers to blue movies (the DAM SIG).

Among those looking for prospective SIG members was Richard S. Holmes of Beltsville, 27, a graduate student studying physics at the University of Maryland. Holmes is coordinator of the National Monty Python SIG, which he started just over a year ago "because I wanted to get in touch with people who liked this sort of weird humor."

The group has 40 members nationally who are interested in the offbeat comedy team, he said, but "aside from greeting each other joyously at regional gatherings, all we do is publish a newsletter."

More successful is OMNI SIG coordinated by Ralph Albers of Falls Church, Va., which meets monthly at Mr. T's Restaurant at Baileys Crossroads. OMNI, he said, stands for "Organization of Mensans Nominally Interested."

"We are Mensans who are intensely interested in everything but not particularly interested in anything," he said. "Each month we invite a proponent of some special interest to address us, who hopes to induce our members to adopt a more productive life style. But we lose very few members."

He said that about 700 members have attended OMNI SIG's functions, which have ranged from programs on nudism to belly-dancing to the trials and tribulations of Washington Post music critic (and fellow Mensan) Joseph McClellan.

Representing one SIG with a serious purpose was Robert Borochoff of Chevy Chase, a computer scientist who is a coordinator of the Human Rights International SIG. On May 1, the SIG will sponsor a demonstration at Lafayette Square in support of Polish Solidarity. It is also studying the problems of "street people" and trying to devise some long-term solutions, Borochoff said.

But, he observed, "Mensa for the most part doesn't get involved in serious things.At serious events, the attendance is quite poor."