What Johnnie Morgan-Lowe does on the weekends is to arrange everybody else's weekends.

She once set up 37 blind dates for a dance. That alone probably qualifies her to run Johnnie's Gang, a club for "singles and retreads," as she puts it.

"They call me madam," she says. But she doesn't just set up those weekend mingling activities for Johnnie's Gang; she joins right in.

Morgan-Lowe's weekends are busy: omelette brunches, tennis nights, bridge games, raft trips, sock hops, fox hunts, bike hikes, a twice-yearly evening of bratwurst and music she calls "Dixieland and dinner," and ski weekends, where she prefers the society in the warming room to the sport on the slopes. Johnnie's Gang may polka at Blob's Park, take in history at Sully Plantation, go camping or just mend fences for a member who lives on a farm.

There are about 2,000 people on the mailing list for Johnnie's Gang; most of the parties listed in her newsletter draw around 100. The average age of the members is 40.

"It's getting the fun people together," says Morgan-Lowe. "People with a good sense of humor, willing to try things. I can't stand these cautious people who are afraid to be laughed at and so concerned with themselves. There's got to be a hard blow for them in life when they realize there's something much more gorgeous and pretty coming along."

Like most organizations, Johnnie's Gang has a hard core of volunteers -- about 30 people who show up for everything and mix. "I tell all my gang," says Morgan-Lowe, " 'You know, each of you is a host or hostess. Anybody comes in that door, the ugliest . . . the fattest . . . whatever, I want you to go up and say hi, and introduce them to at least one other person.' "

Being the matchmaker has its problems. There's the ocasional divorced man who begs Morgan-Lowe not to do him any more favors. And she has to, as she puts it, "protect my girls." When, a few weekends ago on a field trip, a busdriver got fresh with them, Morgan-Lowe looked for a new charter bus company.

She's had some trouble with men this year. After rehearsing for three months, Johnnie's Gang puts on a song-and-dance show every August. For some reason, she says, the men this year were less-than- willing participants: They didn't feel like dressing as showgirls or flappers as they have in previous years.

A sort of chain letter of acquaintance, Johnny's Gang is friends of friends, and that way, says Morgan-Lowe, "we know pretty much what they want, and that they are what they say they are -- they're single or married or divorced or whatever."

A few married people have stayed with Johnnie's Gang, which has been in existence for 20 years. Morgan-Lowe's marriage three years ago to Bob Lowe, a former president of the Washington Ski Club, didn't break up the old gang. "He's a skier; I'm a partier," she says. "But he's very supportive and tolerant of everything -- except one old boyfriend who I guess stepped on his toes."

Although Johnnie's Gang averages six weddings a year, hers wasn't one of them; she met Lowe when she was a project director for the Federal Aviation Administration, where he is publications manager.

She has since stopped working full-time, which probably explains how the Lowes, in addition to all their other activities, can throw a dinner party for 30 people at least once a month.

"When we occasionally find a Saturday alone," says Morgan-Lowe, "we go out for brunch, take a ride, see a new road, go off and look at that, and end up having dinner by ourselves at home. We have a little bottle of champagne. He always says, 'I am not one of the Gang! I'm your husband!' "

On weekends, the Lowes also like house- hunting together and walking around Middleburg. "It could be the two of us and no one else, and he'd be happy," she says.

But, says Morgan-Lowe, "I've always broughthe ai people home. My father was in the military. I know what it's like to go into a place and not have friends. So I've always brought strays home with me." Things really got serious when she belonged to a social sorority at American University: "They would give me $10 or $15 to give a party. That aggravated the hell out of me. I just quit and started doing my own thing."

Having a daughter who's always looking for an excuse for a party, Johnnie Morgan- Lowe's parents often help with the cooking for her get-togethers. They live near her Fairfax home. To explain how they came up with her first name, she says, "I was supposed to be a boy."

"Being an only child, I've always wanted to be part of a big family," she says. "The more you get involved, the more the gang becomes a family of just friends.

"You do things for other people, too. It's not just 'gimme, gimme.' "

This spring, she masterminded a benefit wine-and-cheese party for Children's Hospital. Only problem was, the flier called it "a singles event," and Morgan-Lowe says that's the reason why, when she posted the fliers in stores, they'd be taken down the next day. "You say single, they think of a bunch of rowdy kids. People are prejudiced," she says.

The other Saturday night, Johnnie's Gang rented a bus, went down to St. Marys City and ate dinner at a crab house. On the way back, they stopped at a hotel to have drinks and listen to some music. "It was getting late," says Morgan-Lowe, "and one guy gets up and says, 'Anyone who wants to stay the night, don't use the name James Smith, because 14 couples have already used it.'

"No one stayed," she says when pressed. "I think our bark's bigger than our bite.""