If your sheets are Porthault, your fur Fendi, your jewelry Schlumberger and your money "old," odds are you've bought, or at least heard of, another token of rich exclusivity, a custom-made handbag by Martin Van Schaak.

At prices from $395 to $695 each, there's no jostling and elbowing your way to the handbag counter to get one. Van Schaak not only does not supply his wares to stores, he doesn't even advertise. Instead, word passes privately - and discreetly - when Van Schaak's in town and those with both the means and the taste to be interested, drop in.

"You get addicted to Martin," says Oatsie Charles, a Washingtonian who's known Van Schaak and carried his bags for 20 years.

Van Schaak has been bringing his bags to Washington since 1943, and last week the annual ritual was held again as Van Schaak made himself available to clients at Saks/Jandel in Chevy Chase.

"I came from my sick bed to see these bags, I'd heard so much about them," said Ruth Leffall, wife of a Washington surgeon, who paid $450 for a coral lizard shoulder bag last week. Other fans have included Joan Kennedy, Joan Gardner, Clare Boothe Luce, Connie Mellon, Betsy Bloomingdale and Jacqueline Onassis.

In fact, his clients are something of a secret society.

"I went to a dinner party once and a very attractive lady from Chicago, whom I'd never seen before, came up to me and said, 'I think we have a friend in common,'" recalls Oatsie Charles. "We both had Martin's bags and we've been friends ever since. You always pick out people in airports and restaurants all over the country who have his bags. It's like the old Belgian shoes - you have a common bond. It's just like a little club.

"I have a bag beside me now that's been around the world with the many times. They just don't lose their style. They keep their shape and I'm very hard on bags; they are always stuffed full."

"It's my one extravagance," says Polly Fritchey of Georgetown, who just added another Van Schaak to her collection, which goes back 30 years.

Since he sold his first handbag to the wife of the Dutch ambassador, Van Scaak (who is half Dutch, half Belgian) has been purveying his bags in person to women in New York, Chicago, Philadelphia, Wilmington, Pittsburgh and elsewhere. He usually sells from a hotel room and spends 3 1/2 months each in Texas and California every year taking orders. "I would never allow stores to sell my bags," he says.

"I feel my things are for a group of people with taste and, unfortunately, for the people who also have the means to buy them. Each city in the United States has only a handful of people who can appreciate and buy them, like jewelry."

It's not difficult to spot a Van Schaak once you've had a close look at the 100-plus samples he travels with. Not that he puts any kind of initials on it. ("I wouldn't put my own initials on someone's bag, even if a customer asked me to do it," he says.)

The look (and the cost), he says, is in the workmanship. He keeps six craftsmen busy in New York filling the orders he takes. It's also in the materials - bookbinding leathers, expensive imported skins like lizard and reindeer, brocades, silks and satins.

A typical order: a "swagger" style bag in coral colored lizard with a cigarette pouch inside, five sets of extra handles and satin lining, with the customary lipstick pouch change purse and gold-plated handle-holders. Cost: $595.

Van Schaak says most of his customers still have their first Van Schaak bag and he is constantly getting bags in the mail for repair or restoration.

"Some are in such bad state when I get them," he says, "I feel like sending them back with a note saying 'Why don't you give this to the Salvation Army or your mind,' but some women are so attached to them."

His fans didn't disappoint him last week. Van Schaak may be one of the few people around who can say that with his sale of 17 handbags, business was booming.