For almost 23 years, Joe and Joan Bartley have been welcoming students back from their summer breaks with 50 different types of hamburgers.

It's great to see the familiar faces again," says Mr. Bartley, owner of Bartley's Burger Cottage on Mass. Ave. "During the summer we have mostly tourists, and you just don't get the same personal touch."

That touch is just what the owner says has kept him in business all these years. With the rapid turnover of stores in the Square and the multiplication of trendy eating places and chic boutiques, "students like to see something that's stayed the same," says Mr. B., as he is known to Cottage regulars.

"They feel like they're at home here," he adds. "They can put their feet up. They can borrow money. Mrs. B. and I are sort of The Mom and Dad away from home."

The owners of the Burger Cottage have seen a lot of hungry students come and go in 20 years. "It was tough in the '60s," says Mr. B. "I found it scary knowing that some of the kids eating in my place were the same ones who were rioting a block away." Today's customers are quieter and more subdued, he says, and usually eat in two's and three's instead of large groups.

Tastes have changed slightly, too. "Kids, eat a little lighter and more sophisticated today," Mr. Bartley says, so the Cottage menu now sports salads and such exotica as hummus and tabbouley salad, and potato skins with guacamole. But the specialty of the house has not changed. "People like hamburgers--they always have and they always will," he says.

The secret of the business's longevity, Bartley says, is that it's family-run, with the Bartley's two sons helping in the kitchen and Mrs. B. manning the front counter. "People know they'll get better service that way," he adds.

The burger cottage, which may build a balcony soon to accomodate more customers, also keeps low-key hours by the standards of the Square; it closes early in the evening and remains shuttered on Sundays.

"I won't keep the place open unless a family member is there," Mr. B. says. "I could make much more money if I did, but the extra few hours aren't worth my whole reputation," he adds.

Mom's Home Cooking

That reputation is built on both its homey atmosphere and fresh beef. Bartley explains. First there are the posters--"Bedtime for Brezhnev," the Marx Brothers, and Humphrey Bogart miniatures. And of course the burgers: for just a few dollars, students can choose between a thick, juicy "General Hospital" (guaranteed to get you hooked); the "Nancy Reagan," served on Bartley's best silver; or an "E.T. Burger" complete with genuine Reese's Pieces.

The greatest toward of remaining in the Square so long, Bartley says, comes on Saturdays, when long-time graduates return to the Cottage, sometimes with children in tow.

"Then I realize I've been here a long time," he adds. "They recognize me after all these years and they say, 'You know, Mr. B., all the other places in the Square have changed since my time--but your burgers haven't changed one bit."