It's 10 o'clock on a Saturday morning, and the station wagons and Volkswagens have already started pulling up in front of the Textile Museum at 2320 S St. NW, half a block off Massachusetts Avenue. People emerge from the cars, some carrying large, rolled-up rugs over their shoulders, others sheepishly concealing their treasures in brown supermarket bags. They are coming to the museum's Saturday rug appreciation morning - a sort of show-and-tell, or show-and-betold.

The museum holds these free, open-to-the-public sessions most Saturdays at 10:30. Some have themes, such as "Caucasian Prayer Rugs" or "19th Century Turkish Pile Rugs." but the firstr Saturday of the month is "potpourri." Conservator Clarissa Palmai will tell people how to repair, clean and care for their rugs, silk tapestries and petitpoint chair covers: trustee Harold M. Keshishian will discuss the who, what, where and when - but not the how much - of any rug that shows up.

At a long table at one end of the room, Palmai dragons. "Don't keep it in a plastic bag," she tells the owner. "And if you are going to wear it, you must reline the whole thing with very thin Chinese silk - it's called pongee."

At the other end of the room hung with priceless Chinese rugs, people spread out rugs of every conceivable size, style and condition. There's an air of tense anticipation as Keshishian, a member of a Washington family of renowned rug dealers, surveys the field.

"I don't know everything, now and then I have to pass," he warns the group of about 20. "Who belongs to this rug? And what do you think it is?" "I don't know," says the owner diffidently. "It was in the family . . ." "It's a Lillahan," Keshishian tells him. "Made in the '20s in Persia. It's a great functional utilitarian rug. Let the kids run and jump on it."

Keshishian gets out his glasses to examine a small rug the owner says comes from Mexico. "Mexico? Are you positive it's not from farther south?" Some of the hairs are longer than normally found in Mexican rugs, Keshishian tells him.

"They're probably my dog's hairs," laughs the owner, who readily agrees that the rug may well come from south of Mexico.

A large, reddish rug with a design down the center is "from the Shiraz area of Iran, made about the turn of the century. It's one of the biggest of this type that I've seen," says Keshishian. He points out fantastic animals in the design, plus a lady in a skirt, a six-legged bird and a stylized carnation. "It's a real collectors' piece," He says admiringly. "Try to take care of it. We don't have many left."

Latecomers straggle in, and Keshishian tells them to "Drop your rugs, or they'll get heavy." One late arrival unfolds a rug covered with a stylized flower. "It was made in Turkey during the past 10 years," pronounces Krehishian. "It's a copy of a Persian rug, woven on cotton."

"They told me it was woven on silk," says the owner, "I think I was ripped off."

A couple who have come all the way from Pennsylvania for the session stand near their acquisition - mellowed rose rug decorated with large, realistic-looking lions, a crown and a lot of calligraphy. Reading the script, Keshishian proclaims that the rug was made in 1808. "My father was born in 1310, and that's the Islamic equivalent of 1894," he explains. "This is dated 1314." The motif, says Keshishian, shows great French influence. "This was at a time when it was fashionable to speak French and to have French furniture."

A runner with a diagonal design containing stylized camels provokes some puzzlement. It's from the southern half of the Caucasus, Keshishian is sure, but he can't place the exact spot. "A girl from one village may have married a boy from another. She remembers how her mothe taught her to weave rugs, but now her mother-in-law is telling her, too. You get all illegitimate rug."

Keshishian passes from rug to rug, pronouncing one "in an early embryonic state of decay but still quite handsome." Another, he warns, should be trod on only lightly. He tells the owner of a rumpled, beige-and-white rug: "It was made in Belgium or Italy on a machine." "So you think so?" asks the disappointed owner. "I know so," replies Keshishian gently but firmly.

Most of the people have rolled up their rugs and departed, and Keshishian smiles with satisfaction. "They were a nice crowd today.Sometimes we get people who know it all. We've discovered some great rugs at these sessions. Once a man came in off the street with a fantastic 17th-century Oushak rug. I almost fell over. Then there's the other side, like that young man today with the machine-made rug he probably thought was a family heirloom. I always try to tell them as nicely as I can."